SNAP-4 Service Advanced Features

RPC log history (enabled by default) records all the RPC requests (from snap_rpc.py and spdk_rpc.py) sent to the SNAP application and the RPC response for each RPC requests in a dedicated log file, /var/log/snap-log/rpc-log. This file is visible outside the container (i.e., the log file's path on the DPU is /var/log/snap-log/rpc-log as well).

The SNAP_RPC_LOG_ENABLE env can be used to enable (1) or disable (0) this feature.

SR-IOV configuration depends on the kernel version and must be handled carefully to ensure device visibility and system stability across both hypervisor and DPU orchestrators.

To ensure a safe and stable SR-IOV setup, follow these steps:

1. Preconfigure VF controllers on the DPU – Before configuring SR-IOV on the host, ensure that the DPU is properly configured with all required VF controllers already created and opened.

   • VF functions are always visible and configurable on the DPU side. Use the following command to verify:

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     snap_rpc.py emulation_function_list --all
             

   • Confirm that the configuration meets your requirements.

     • Check the number of resources allocated for the PF, specifically MSIX and queues (queried using snap_rpc.py virtio_blk_controller_list RPC output, field free_queues and free_msix ) are enough to satisfy your needs for all underlying VFs.

     • Use dynamic MSIX if needed and supported.

   • Once host-side configuration begins, further modifications may not be possible.

2. Disable autoprobing with sriov_drivers_autoprobe=0 – In deployments with many virtual devices, autoprobing must be disabled to ensure stable device discovery. Failing to disable autoprobing may result in:

   • Incomplete device visibility

   • Missing virtual disks

   • System hangs during initialization

   • Unreliable behavior in large-scale environments (more than 100 VFs)

     Tip

     Recommended configuration for large-scale deployments:

     • Disable autoprobe:

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       echo 0 > /sys/bus/pci/devices/<BDF>/sriov_drivers_autoprobe
               

     • Manually bind the VFs to drivers using tools such as driverctl, or by writing to bind/unbind in sysfs.

3. Configure SR-IOV on the host – For small-scale deployments (fewer than 100 VFs), use the sriov_totalvfs entry:

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   echo <number_of_vfs> > /sys/bus/pci/devices/<BDF>/sriov_totalvfs
           

   For newer drivers, use:

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   echo <number_of_vfs> > /sys/bus/pci/devices/<BDF>/sriov_numvfs
           

   Note

   After SR-IOV configuration, no disks appear in the hypervisor by default. Disks are only visible inside VMs once the corresponding PCIe VF is assigned to the VM via a virtualization manager (e.g., libvirt, VMware). To use the device directly from the hypervisor, manually bind the VF to the appropriate driver.

Additional notes:

• Hot-plugged PFs do not support SR-IOV.

• For deployments requiring more than 127 VFs, add the following kernel parameter to the host’s boot command line:

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  pci=assign-busses
          

  Without this, the host may log errors such as:

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  pci 0000:84:00.0: [1af4:1041] type 7f class 0xffffff
  pci 0000:84:00.0: unknown header type 7f, ignoring device
          

  These errors prevent the virtio driver from probing the device.

SNAP-direct allows SNAP applications to transfer data directly from the host memory to remote storage without using any staging buffer inside the DPU.

SNAP enables the feature according to the SPDK BDEV configuration only when working against an SPDK NVMe-oF RDMA block device.

To enable zero copy, set the environment variable (as it is enabled by default):

            

            
SNAP_RDMA_ZCOPY_ENABLE=1
        

For more info refer to SNAP-4 Service Environment Variables.

NVMe/TCP Zero Copy is implemented as a custom NVDA_TCP transport in SPDK NVMe initiator, and it is based on a new XLIO socket layer implementation.

The implementation is different for Tx and Rx:

• The NVMe/TCP Tx Zero Copy is similar between RDMA and TCP in that the data is sent from the host memory directly to the wire without an intermediate copy to Arm memory

• The NVMe/TCP Rx Zero Copy allows achieving partial zero copy on the Rx flow by eliminating copy from socket buffers (XLIO) to application buffers (SNAP). But data still must be DMA'ed from Arm to host memory.

To enable NVMe/TCP Zero Copy, use SPDK v22.05.nvda --with-xlio (v22.05.nvda or higher).

To enable SNAP TCP XLIO Zero Copy:

1. SNAP container: Set the environment variables and resources in the YAML file:

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   resources:
     requests:
       memory: "4Gi"
       cpu: "8"
     limits:
       hugepages-2Mi: "4Gi"
       memory: "6Gi"
       cpu: "16"
    
   ## Set according to the local setup
   env:
     - name: APP_ARGS
       value: "--wait-for-rpc"
     - name: SPDK_XLIO_PATH
       value: "/usr/lib/libxlio.so"
           

2. SNAP sources: Set the environment variables and resources in the relevant scripts

   1. In run_snap.sh, edit the APP_ARGS variable to use the SPDK command line argument --wait-for-rpc:

      run_snap.sh

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      APP_ARGS="--wait-for-rpc"
              

   2. In set_environment_variables.sh, uncomment the SPDK_XLIO_PATH environment variable:

      set_environment_variables.sh

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      export SPDK_XLIO_PATH="/usr/lib/libxlio.so"
              

            

            
[dpu] spdk_rpc.py bdev_nvme_set_options --transport-ack-timeout 12
        

Expose an NVMe-oF subsystem with one namespace by using a TCP transport type on the remote SPDK target.

            

            
[dpu] spdk_rpc.py sock_set_default_impl -i xlio
[dpu] spdk_rpc.py framework_start_init
[dpu] spdk_rpc.py bdev_nvme_set_options --transport-ack-timeout 12
[dpu] spdk_rpc.py bdev_nvme_attach_controller -b nvme0 -t nvda_tcp -a 3.3.3.3 -f ipv4 -s 4420 -n nqn.2023-01.io.nvmet
[dpu] snap_rpc.py nvme_subsystem_create --nqn nqn.2023-01.com.nvda:nvme:0
[dpu] snap_rpc.py nvme_namespace_create -b nvme0n1 -n 1 --nqn nqn. 2023-01.com.nvda:nvme:0 --uuid 16dab065-ddc9-8a7a-108e-9a489254a839
[dpu] snap_rpc.py nvme_controller_create --nqn nqn.2023-01.com.nvda:nvme:0 --ctrl NVMeCtrl1 --pf_id 0 --suspended --num_queues 16
[dpu] snap_rpc.py nvme_controller_attach_ns -c NVMeCtrl1 -n 1 
[dpu] snap_rpc.py nvme_controller_resume -c NVMeCtrl1 -n 1
 
[host] modprobe -v nvme
[host] fio --filename /dev/nvme0n1 --rw randrw --name=test-randrw --ioengine=libaio --iodepth=64 --bs=4k --direct=1 --numjobs=1 --runtime=63 --time_based --group_reporting --verify=md5
        

The SPDK version that comes with SNAP supports hardware encryption/decryption offload. To enable AES/XTS, follow the instructions under section "Modifying SF Trust Level to Enable Encryption".

Zero Copy (SNAP-direct) with Encryption

SNAP offers support for zero copy with encryption for bdev_nvme with an RDMA transport.

mlx5_scan_accel_module

Accepts a list of devices to use for the crypto operation provided in the --allowed-devs parameter. If no devices are specified, then the first device which supports encryption is used.

For best performance, it is recommended to use the devices with the largest InfiniBand MTU (4096). The MTU size can be verified using the ibv_devinfo command (look for the max and active MTU fields). Normally, the mlx5_2 device is expected to have an MTU of 4096 and should be used as an allowed crypto device.

Command parameters:

accel_crypto_key_create

Creates crypto key. One key can be shared by multiple bdevs.

Command parameters:

bdev_nvme_attach_controller

Creates NVMe block device.

Command parameters:

bdev_crypto_create

This RPC creates a virtual crypto block device which adds encryption to the base block device.

Command parameters:

SPDK Crypto Example

The following is an example of a configuration with a crypto virtual block device created on top of bdev_nvme with RDMA transport and zero copy support:

            

            
[dpu] # spdk_rpc.py mlx5_scan_accel_module --allowed-devs "mlx5_2" --enable-driver
[dpu] # spdk_rpc.py framework_start_init
[dpu] # spdk_rpc.py accel_crypto_key_create -c AES_XTS -k 00112233445566778899001122334455 -e 11223344556677889900112233445500 -n test_dek
[dpu] # spdk_rpc.py bdev_nvme_attach_controller -b nvme0 -t rdma -a 1.1.1.1 -f ipv4 -s 4420 -n nqn.2016-06.io.spdk:cnode0
[dpu] # spdk_rpc.py bdev_crypto_create nvme0n1 crypto_0 -n test_dek
[dpu] # snap_rpc.py spdk_bdev_create crypto_0
[dpu] # snap_rpc.py nvme_subsystem_create --nqn nqn.2023-05.io.nvda.nvme:0
[dpu] # snap_rpc.py nvme_controller_create --nqn nqn.2023-05.io.nvda.nvme:0 --pf_id 0 --ctrl NVMeCtrl0 --suspended
[dpu] # snap_rpc.py nvme_namespace_create –nqn nqn.2023-05.io.nvda.nvme:0 --bdev_name crypto_0 –-nsid 1 -–uuid 263826ad-19a3-4feb-bc25-4bc81ee7749e
[dpu] # snap_rpc.py nvme_controller_attach_ns –-ctrl NVMeCtrl0 --nsid 1
[dpu] # snap_rpc.py nvme_controller_resume –-ctrl NVMeCtrl0
        

Live migration is a standard process supported by QEMU which allows system administrators to pass devices between virtual machines in a live running system. For more information, refer to QEMU VFIO Device Migration documentation.

Live migration is supported for SNAP virtio-blk devices in legacy and standard VFIO modes. Legacy mode uses drivers like NVIDIA's proprietary vDPA-based Live Migration Solution, while standard mode leverages the latest kernel capabilities using the virtio-vfio-pci kernel driver. Legacy mode can be enabled/disabled using the environment variable `VIRTIO_CTRL_VDPA_ADMIN_Q` (enabled by default).

Software Requirements for Standard VFIO

• Kernel – 6.16-rc3+ (using virtio-vfio-pci driver)

• QEMU – 9.2+

• libvirt – 10.6+

SNAP Configuration

1. Set the environment variable VIRTIO_CTRL_VDPA_ADMIN_Q to 1 (default) for legacy or 0 for standard VFIO mode.

2. Create a PF Controller with Admin Queue (common to both modes):

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   snap_rpc.py virtio_blk_controller_create --admin_q …
           

Live upgrade enables updating the SNAP image used by a container without causing SNAP container downtime.

While newer SNAP releases may introduce additional content, potentially causing behavioral differences during the upgrade, the process is designed to ensure backward compatibility. Updates between releases within the same sub-version (e.g., 4.0.0-x to 4.0.0-y) should proceed without issues.

However, updates across different major or minor versions may require changes to system components (e.g., firmware, BFB), which may impact backward compatibility and necessitate a full reboot post update. In those cases, live updates are unnecessary.

Live Upgrade Prerequisites

To enable live upgrade, perform the following modifications:

1. Allocate double hugepages for the destination and source containers.

2. Make sure the requested amount of CPU cores is available.

   The default YAML configuration sets the container to request a CPU core range of 8-16. This means that the container is not deployed if there are fewer than 8 available cores, and if there are 16 free cores, the container utilizes all 16.

   For instance, if a container is currently using all 16 cores and, during a live upgrade, an additional SNAP container is deployed. In this case, each container uses 8 cores during the upgrade process. Once the source container is terminated, the destination container starts utilizing all 16 cores.

   Note

   For 8-core DPUs, the .yaml must be edited to the range of 4-8 CPU cores.

3. Change the name of the doca_snap.yaml file that describes the destination container (e.g., doca_snap_new.yaml ) so as to not overwrite the running container .yaml.

4. Change the name of the new .yaml pod and container on lines 16 and 20, respectively (e.g., snap-new).

5. Deploy the the destination container by copying the new yaml (e.g., doca_snap_new.yaml ) to kubelet.

SNAP Container Live Upgrade Procedure

1. Follow the steps in section "Live Upgrade Prerequisites" and deploy the destination SNAP container using the modified yaml file.

2. Query the source and destination containers:

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   crictl ps -r
           

3. Check for SNAP started successfully in the logs of the destination container, then copy the live update from the container to your environment.

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   [dpu] crictl logs -f <dest-container-id>
   [dpu] crictl exec <dest-container-id> cp /opt/nvidia/nvda_snap/bin/live_update.py /etc/nvda_snap/
           

4. Run the live_update.py script to move all active objects from the source container to the destination container:

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   [dpu] cd /etc/nvda_snap
   [dpu] ./live_update.py -s <source-container-id> -d <dest-container-id>
           

   Info

   The live update tool also supports transitioning between the SNAP source package service and the SNAP container service (and vice versa). Use -s 0 to indicate that the source (original process) is running from the SNAP source package.

5. After the script completes, the live update process also completes, delete the source container by removing the YAML from kubelet tool:

   Note

   To post RPCs, use the crictl tool:

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   crictl exec -it <container-id X> snap_rpc.py <RPC-method>
   crictl exec -it <container-id Y> spdk_rpc.py <RPC-method>
           

   Note

   To automate the SNAP configuration (e.g., following failure or reboot) as explained in section "Automate SNAP Configuration (Optional)", spdk_rpc_init.conf and snap_rpc_init.conf must not include any configs as part of the live upgrade. Then, once the transition to the new container is done, spdk_rpc_init.conf and snap_rpc_init.conf can be modified with the desired configuration.

SNAP Container Live Upgrade Commands

The live upgrade process allows moving SNAP controllers and SPDK block devices between containers while minimizing host VM disruption.

The upgrade is done using a dedicated live update tool, which iterates over all active emulation functions and performs the following steps:

1. Suspend controller (admin only). On the source container, suspend the controller to admin-only mode. This ensures the controller no longer processes admin commands from the host driver, avoiding state changes during the handover. I/O traffic continues, so downtime has not started yet.

   • NVMe example:

     NMVe exmaple:

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     snap_rpc.py nvme_controller_suspend --ctrl NVMeCtrl0VF0 --admin_only
             

   • Virtio-blk example:

     Virtio-blk Example

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     snap_rpc.py virtio_blk_controller_suspend --ctrl [ctrl_name] --events_only
             

2. Preparation on destination container. On the destination container, create all required objects for the new controller, including attaching the backend device.

   • NVMe example:

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     spdk_rpc.py bdev_nvme_attach_controller ...
     snap_rpc.py nvme_subsystem_create ...
     snap_rpc.py nvme_namespace_create -n 1 ...
             

   • Virtio-blk example:

     Virtio-blk Example

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     spdk_rpc.py bdev_nvme_attach_controller ...
             

3. Create suspended controller (as listener). On the destination container, create the controller in a suspended state and mark it as a listener for a live update notification from the source container. At this point, the controller in the source container is still handling I/O, so downtime has not started yet.

   • NVMe example:

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     snap_rpc.py nvme_controller_create --pf_id 0 --vf_id 0 --ctrl NVMeCtrl0VF0 --live_update_listener --suspended ...
     snap_rpc.py nvme_controller_attach_ns -c NVMeCtrl0VF0 -n 1
             

   • Virtio-blk example:

     Virtio-blk Example

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     snap_rpc.py virtio_blk_controller_create  --pf_id 0 --vf_id 0 --ctrl VBLKCtrl0VF0 ...
             

4. Suspend and notify. On the source container, suspend the controller using the --live_update_notifier flag. This triggers the start of downtime and sends a notification to the destination container. Once suspended, the controller on the destination container resumes and starts handling I/O. This marks the end of downtime.

   • NVMe example:

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     snap_rpc.py nvme_controller_suspend --ctrl NVMeCtrl0VF0 --live_update_notifier --timeout_ms
             

   • Virtio-blk example:

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     snap_rpc.py virtio_blk_controller_suspend --ctrl [ctrl_name] --events_only
             

5. Cleanup source container. After the migration is complete, clean up any remaining controller objects on the source container.

   Note

   The PF controller must remain present in the source container until all related virtual functions (VFs) have been removed.

   • NVMe example:

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     snap_rpc.py nvme_controller_detach_ns ...
     spdk_rpc.py bdev_nvme_detach_controller ...
     snap_rpc.py nvme_namespace_destroy ...
     snap_rpc.py nvme_controller_destroy ...
             

   • Virtio-blk example:

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     snap_rpc.py virtio_blk_controller_suspend --ctrl [ctrl_name] --events_only
             

Message Signaled Interrupts eXtended (MSIX) is an interrupt mechanism that allows devices to use multiple interrupt vectors, providing more efficient interrupt handling than traditional interrupt mechanisms such as shared interrupts. In Linux, MSIX is supported in the kernel and is commonly used for high-performance devices such as network adapters, storage controllers, and graphics cards. MSIX provides benefits such as reduced CPU utilization, improved device performance, and better scalability, making it a popular choice for modern hardware.

However, proper configuration and management of MSIX interrupts can be challenging and requires careful tuning to achieve optimal performance, especially in a multi-function environment as SR-IOV.

By default, BlueField distributes MSIX vectors evenly between all virtual PCIe functions (VFs). This approach is not optimal as users may choose to attach VFs to different VMs, each with a different number of resources. Dynamic MSIX management allows the user to manually control of the number of MSIX vectors provided per each VF independently.

Dynamic MSIX management is built from several configuration steps:

1. At this point, and in any other time in the future when no VF controllers are opened (sriov_numvfs=0), all PF-related MSIX vectors can be reclaimed from the VFs to the PF's free MSIX pool.

2. User must take some of the MSIX from the free pool and give them to a certain VF during VF controller creation.

3. When destroying a VF controller, the user may choose to release its MSIX back to the pool.

Once configured, the MSIX link to the VFs remains persistent and may change only in the following scenarios:

• User explicitly requests to return VF MSIXs back to the pool during controller destruction.

• PF explicitly reclaims all VF MSIXs back to the pool.

• Arm reboot (FE reset/cold boot) has occurred.

To emphasize, the following scenarios do not change MSIX configuration:

• Application restart/crash.

• Closing and reopening PF/VFs without dynamic MSIX support.

The following is an NVMe example of dynamic MSIX configuration steps (similar configuration also applies for virtio-blk):

1. Reclaim all MSIX from VFs to PF's free MSIX pool:

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   snap_rpc.py nvme_controller_vfs_msix_reclaim <CtrlName>
           

2. Query the controller list to get information about the resources constraints for the PF:

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   # snap_rpc.py nvme_controller_list -c <CtrlName>
   …     'free_msix': 100,
   …     'free_queues': 200,
   …     'vf_min_msix': 2,
   …     'vf_max_msix': 64,
   …     'vf_min_queues': 0,
   …     'vf_max_queues': 31,
   …
           

   Where:

   • free_msix stands for the number of total MSIX available in the PF's free pool, to be assigned for VFs, through the parameter vf_num_msix (of the <protocol>_controller_create RPC).

   • free_queues stands for the number of total queues (or "doorbells") available in the PF's free pool, to be assigned for VFs, through the parameter num_queues (of the <protocol>_controller_create RPC).

   • vf_min_msix and vf_max_msix together define the available configurable range of vf_num_msix parameter value which can be passed in <protocol>_controller_create RPC for each VF.

   • vf_min_queues and vf_max_queues together define the available configurable range of num_queues parameter value which can be passed in <protocol>_controller_create RPC for each VF.

3. Distribute MSIX between VFs during their creation process, considering the PF's limitations:

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   snap_rpc.py nvme_controller_create_ --vf_num_msix <n> --num_queues <m> …
           

   Note

   It is strongly recommended to specify both vf_num_msix and num_queues when creating a VF controller. Supplying only one of these parameters can cause a mismatch between MSI-X allocation and queue configuration, potentially leading to controller or driver malfunctions.

   Tip

   In the NVMe protocol, MSI-X vectors are allocated per completion queue (CQ). It is therefore recommended to assign one MSI-X from the PF's global pool (free_msix) for each queue.

   In the virtio protocol, MSI-X vectors are allocated per virtqueue, with one additional MSI-X required for BAR configuration change notifications. It is therefore recommended to assign one MSI-X from the PF's global pool for each queue, plus one additional MSI-X for configuration notifications.

   In summary, the best practice for queues/MSIX ratio configuration is:

   • For NVMe – num_queues = vf_num_msix

   • For virtio – num_queues = vf_num_msix-1

4. Upon VF teardown, release MSIX back to the free pool:

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   snap_rpc.py nvme_controller_destroy_ --release_msix …
           

5. Set SR-IOV on the host driver:

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   echo <N> > /sys/bus/pci/devices/<BDF>/sriov_numvfs
           

   Note

   It is strongly recommended to open all VF controllers in SNAP before binding VFs to the host or guest driver. This ensures that, in the event of a configuration error (e.g., insufficient MSIX or queue resources for all VFs) the configuration remains reversible, as the resources are still modifiable.

   If VFs are bound to the driver before all VF configuration is complete, the driver may attempt to use resources from already configured VFs. However, if resources are insufficient, the driver will not be able to utilize them all. This scenario can lead to a host deadlock, which in the worst case may only be recoverable through a cold boot.

   Note

   There are several ways to configure dynamic MSIX safely (without VF binding):

   1. Disable kernel driver automatic VF binding to kernel driver:

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      # echo 0 > /sys/bus/pci/devices/sriov_driver_autoprobe
              

      After finishing MSIX configuration for all VFs, they can then be bound to VMs, or even back to the hypervisor:

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      echo "0000:01:00.0" > /sys/bus/pci/drivers/nvme/bind
              

   2. Use VFIO driver (instead of kernel driver) for SR-IOV configuration.

      For example:

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      # echo 0000:af:00.2 > /sys/bus/pci/drivers/vfio-pci/bind				# Bind PF to VFIO driver
      # echo 1 > /sys/module/vfio_pci/parameters/enable_sriov
      # echo <N> > /sys/bus/pci/drivers/vfio-pci/0000:af:00.2/sriov_numvfs	# Create VFs device for it
              

The recovery feature enables the restoration of controller state after the SNAP application terminates—either gracefully or unexpectedly (e.g., due to kill -9).

NVMe Recovery

NVMe recovery enables the restoration of an NVMe controller after a SNAP application terminates, whether gracefully or due to a crash (e.g., kill -9).

To perform NVMe recovery:

1. Re-create the controller in a suspended state using the exact same configuration as before the crash (including the same bdevs, number of queues, namespaces, and namespace UUIDs).

2. Resume the controller only after all namespaces have been attached.

The recovery process uses shared memory files located under /dev/shm on the BlueField to restore the controller's internal state. These files are deleted when the BlueField is reset, meaning recovery is not supported after a BF reset.

Virtio-blk Crash Recovery

To use virtio-blk recovery, the controller must be re-created with the same configuration as before the crash (i.e. the same bdevs, num queues, etc).

The following options are available to enable virtio-blk crash recovery.

Virtio-blk Crash Recovery with --force_in_order

For virtio-blk crash recovery with --force_in_order, disable the VBLK_RECOVERY_SHM environment variable and create a controller with the --force_in_order argument.

In virtio-blk SNAP, the application is not guaranteed to recover correctly after a sudden crash (e.g., kill -9).

To enable the virtio-blk crash recovery, set the following:

            

            
snap_rpc.py virtio_blk_controller_create --force_in_order …
        

Virtio-blk Crash Recovery without --force_in_order

For virtio-blk crash recovery without --force_in_order, enable the VBLK_RECOVERY_SHM environment variable and create a controller without the --force_in_order argument.

Virtio-blk recovery allows the virtio-blk controller to be recovered after a SNAP application is closed whether gracefully or after a crash (e.g., kill -9).

To use virtio-blk recovery without --force_in_order flag. VBLK_RECOVERY_SHM must be enabled, the controller must be recreated with the same configuration as before the crash (i.e., same bdevs, num queues, etc).

When VBLK_RECOVERY_SHM is enabled, virtio-blk recovery uses files on the BlueField under /dev/shm to recover the internal state of the controller. Shared memory files are deleted when the BlueField is reset. For this reason, recovery is not supported after BlueField reset.

SNAP Configuration Recovery

SNAP can store its configuration as defined by user RPCs and, upon restart, reload it from a configuration JSON file. This mechanism is intended for recovering a previously configured SNAP state — it cannot be used for the initial configuration.

Usage:

1. Set the environment variable SNAP_RPC_INIT_CONF_JSON to the directory path where the configuration file will be stored.

2. The configuration file, snap_config.json, is created in this directory after all changes in your script have been successfully applied.

3. If a new configuration (different from the pre-shutdown configuration) is required after restarting SNAP, delete the existing snap_config.json file before applying the new settings.

When this method is used, there is no need to re-run snap RPCs or set RPCs in init files after the initial configuration — SNAP will automatically load the saved configuration from the SNAP_RPC_INIT_CONF_JSON path. This approach is recommended for fast recovery.

Improving SNAP Recovery Time

The following table outlines features designed to accelerate SNAP initialization and recovery processes following termination.

            

            
spdk_rpc.py save_config > config.json
        

            

            
{
	"method": "mlx5_scan_accel_module",
	"params": {
	 "qp_size": 64,
	 "cq_size": 1024,
 	 "num_requests": 2048,
 	 "enable_driver": false,
 	 "split_mb_blocks": 0,
 	 "siglast": false,
 	 "qp_per_domain": false,
	 "disable_signature": true,
	 "disable_crypto": true,
	 "enable_module": false
	}
        

The Watchdog and Heartbeat Monitoring feature is an experimental reliability mechanism designed to enhance the robustness of the system by automatically detecting and recovering from application hangs, crashes, or unresponsive components. This mechanism minimizes service disruption by triggering recovery procedures without requiring manual intervention.

The heartbeat system functions as a periodic signal emitted by the SNAP service to indicate its operational status. These signals serve as an indicator that the service is active and functioning as expected.

A dedicated watchdog component monitors the presence and frequency of heartbeat signals. If the heartbeat is not received within a predefined timeout interval, the watchdog determines that the monitored component is unresponsive and initiates a predefined recovery action.

The typical sequence of operations is as follows:

1. A SNAP component becomes unresponsive due to a crash, hang, or other failure condition.

2. The watchdog detects the absence of the expected heartbeat signal.

3. A recovery action is automatically triggered.

4. The SNAP service is restarted, and previously configured virtual disk states are restored.

5. Normal operation resumes.

The entire recovery process is designed to complete within a few seconds, thereby minimizing downtime.

Configuring the Watchdog

The behavior of the Watchdog and Heartbeat Monitoring system is configurable through environment variables. These variables allow the user to specify parameters such as heartbeat intervals, timeouts, and recovery policies without requiring changes to the application code.

Running the Watchdog

To initiate the watchdog service while the SNAP application is running, execute the following command:

            

            
./snap_watchdog.py --daemon
        

This command launches the watchdog in the background, where it continuously monitors the health of the SNAP service and initiates recovery procedures as necessary.

The I/O Core Multiplexer (MP) is a configurable mechanism that determines how I/O requests from a single source are distributed across the available DPU cores. This feature is critical for optimizing performance based on application-specific needs, particularly in scenarios involving high I/O workloads.

The multiplexer offers two policy modes:

• None (Default) – All I/O operations originating from a single source are processed by a single DPU core. I/O sources are distributed across DPU cores in a balanced manner.

  • Recommended for: Low-latency environments

  • Optimization focus: I/O latency

• (Weighted) Round Robin – I/O requests from a single source are distributed across multiple DPU cores in a round-robin sequence. If the backend supports per-core weight configuration (e.g., SPDK NVMe-oF bdev), the distribution follows those weights. Otherwise, the I/Os are spread evenly.

  • Recommended for: Bandwidth-intensive environments or systems with low per-core backend throughput (e.g., TCP-based backends)

  • Optimization focus: I/O bandwidth

To configure the IO/Core Multiplexer policy, users need to set the IO_CORE_DISTRIBUTION_POLICY environment variable. The available options are:

• none – Refers to the default policy where all I/Os from a single source are handled by a single DPU core

• weighted_rr – Refers to the (Weighted) Round Robin policy, distributing I/Os across multiple cores

  Note

  weighted_rr policy is not supported for virtio-blk.

The SNAP ML Optimizer is a performance-tuning utility that dynamically adjusts polling parameters within the SNAP I/O subsystem. It is designed to improve controller throughput by identifying the optimal configuration based on current hardware, workload patterns, and system constraints.

How it works:

1. During runtime, the optimizer iteratively modifies internal configuration parameters (referred to as "actions").

2. After each configuration change, it measures the resulting system performance (referred to as the "reward").

3. Using predictive modeling, the optimizer determines the most promising configuration to evaluate next, allowing it to converge on an optimal setup efficiently.

This approach eliminates the need to exhaustively test all possible combinations, significantly reducing tuning time while ensuring performance gains.

SNAP ML Optimizer Preparation Steps

Machine Requirements

The device should be able to SSH to the BlueField:

• Python 3.10 or above

• At least 6 GB of free storage

Setting Up SNAP ML Optimizer

To set up the SNAP ML optimizer:

1. Copy the snap_ml folder from the container to the shared nvda_snap folder and then to the requested machine:

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   crictl exec -it $(crictl ps -s running -q --name snap) cp -r /opt/nvidia/nvda_snap/bin/snap_ml /etc/nvda_snap/
           

2. Change directory to the snap_ml folder:

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   cd tools/snap_ml
           

3. Create a virtual environment for the SNAP ML optimizer.

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   python3 -m venv snap_ml
           

   This ensures that the required dependencies are installed in an isolated environment.

4. Activate the virtual environment to start working within this isolated environment:

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   source snap_ml/bin/activate 
           

5. Install the Python package requirements:

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   pip3 install --no-cache-dir -r requirements.txt
           

   This may take some time depending on your system's performance.

6. Run the SNAP ML Optimizer.

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   python3 snap_ml.py --help 
           

   Use the --help flag to see the available options and usage information:

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   --version Show the version and exit. 
   -f, --framework <TEXT> Name of framework (Recommended: ax , supported: ax, pybo). 
   -t, --total-trials <INTEGER> Number of optimization iterations. The recommended range is 25-60. 
   --filename <TEXT> where to save the results (default: last_opt.json). 
   --remote <TEXT> connect remotely to the BlueField card, format: <bf_name>:<username>:<password> 
   --snap-rpc-path <TEXT> Snap RPC prefix (default: container path). 
   --log-level <TEXT> CRITICAL | ERROR | WARN | WARNING | INFO | DEBUG 
   --log-dir <TEXT> where to save the logs. 
           

SNAP ML Optimizer Related RPCs

snap_actions_set

The snap_actions_set command is used to dynamically adjust SNAP parameters (known as "actions") that control polling behavior. This command is a core feature of SNAP-AI tools, enabling both automated optimization for specific environments and workloads, as well as manual adjustment of polling parameters.

Command parameters:

snap_reward_get

The snap_reward_get command retrieves performance counters, specifically completion counters (or "reward"), which are used by the optimizer to monitor and enhance SNAP performance.

No parameters are required for this command.

Run the ML Optimizer

To optimize SNAP’s parameters for your environment, use the following command:

            

            
python3 snap_ml.py --framework ax --total-trials 40 --filename example.json --remote <bf_hostname>:<username>:<password> --log-dir <log_directory> 
        

Results and Post-optimization Actions

Once the optimization process is complete, the tool automatically applies the optimized parameters. These parameters are also saved in a example.json file in the following format:

            

            
{ 
    "poll_size": 30, 
    "poll_ratio": 0.6847347955107689, 
    "max_inflights": 32768, 
    "max_iog_batch": 512, 
    "max_new_ios": 32 
} 
        

Additionally, the tool documents all iterations, including the actions taken and the rewards received, in a timestamped file named example_<timestamp>.json.

Applying Optimized Parameters Manually

Users can apply the optimized parameters on fresh instances of SNAP service by explicitly calling the snap_actions_set RPC with the optimized parameters as follows:

            

            
snap_rpc.py snap_actions_set –poll_size 30 –poll_ratio 0.6847 --max_inflights 32768 –max_iog_batch 512 –max_new_ios 32 
        

Deactivating Python Environment

Once users are done using the SNAP ML Optimizer, they can deactivate the Python virtual environment by running:

            

            
deactivate
        

Plugins are modular components or add-ons that enhance the functionality of the SNAP application. They integrate seamlessly with the main software, allowing additional features without requiring changes to the core codebase. Plugins are designed for use only with the source package, as it allows customization during the build process, such as enabling or disabling plugins as needed.

In containerized environments, the SNAP application is shipped as a pre-built binary with a fixed configuration. Since the binary in the container is precompiled, adding or removing plugins is not possible. The containerized software only supports the plugins included during its build. For environments requiring plugin flexibility, such as adding custom plugins, the source package must be used.

To build a SNAP source package with a plugin, perform the following instead of following the basic build steps :

1. Move to the sources folder. Run:

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   cd /opt/nvidia/nvda_snap/src/
           

2. Build the sources with plugin to be enabled. Run:

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   meson setup /tmp/build -Denable-bdev-null=true -Denable-bdev-malloc=true
           

3. Compile the sources. Run:

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   meson compile -C /tmp/build
           

4. Install the sources. Run:

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   meson install -C /tmp/build
           

5. Configure the SNAP environment variables and run SNAP service as explained in sections "Configure SNAP Environment Variables" and "Run SNAP Service".

Bdev

SNAP supports various types of block devices (bdev), offering flexibility and extensibility in interacting with storage backends. These bdev plugins provide different storage emulation options, allowing customization without requiring modifications to the core software.

SPDK

• SPDK is the default plugin used by SNAP. If no specific plugin is explicitly specified, SNAP will default to using SPDK for block device operations.

• For more information, refer to spdk_bdev.

Malloc

• The Malloc plugin is intended for performance analysis and debugging purposes only; it is not suitable for production use

• It creates a memory-backed block device by allocating a buffer in memory and exposing it as a block device

• Since data is stored in memory, it is lost when the system shuts down

• This plugin can be enabled using the enable-bdev-malloc build option

Malloc configuration example:

1. Create Malloc bdev and use it with an NVMe controller:

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   # snap_rpc.py snap_bdev_malloc_create --bdev test 64 512
   # snap_rpc.py nvme_subsystem_create -s nqn.2020-12.mlnx.snap
   # snap_rpc.py nvme_namespace_create -s nqn.2020-12.mlnx.snap -t malloc -b test -n 1
   # snap_rpc.py nvme_controller_create --pf_id=0 -s nqn.2020-12.mlnx.snap --mdts=7
   # snap_rpc.py nvme_controller_attach_ns -c NVMeCtrl1 -n 1
           

2. Delete Malloc bdev:

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   # snap_rpc.py snap_bdev_malloc_destroy test
           

3. Resize Malloc bdev:

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   # snap_rpc.py snap_bdev_malloc_resize test 32
           

   This removes the existing bdev and creates a new one with the specified size. Data on the existing bdev will be lost.

NULL

• The NULL plugin is designed for performance analysis and debugging purposes and is not intended for production use.

• It acts as a dummy block device, accepting I/O requests and emulating a block device without performing actual I/O operations.

• It is useful for testing or benchmarking scenarios that do not involve real storage devices.

• The plugin consumes minimal system resources.

• It can be enabled using the enable-bdev-null build option.

NULL configuration example:

1. Create a NULL bdev and use it with an NVMe controller:

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   # snap_rpc.py snap_bdev_null_create_dbg test 1 512
   # snap_rpc.py nvme_subsystem_create -s nqn.2020-12.mlnx.snap
   # snap_rpc.py nvme_namespace_create -s nqn.2020-12.mlnx.snap -t malloc -b test -n 1
   # snap_rpc.py nvme_controller_create --pf_id=0 -s nqn.2020-12.mlnx.snap --mdts=7
   # snap_rpc.py nvme_controller_attach_ns -c NVMeCtrl1 -n 1
           

2. Delete the NULL bdev:

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   # snap_rpc.py snap_bdev_null_destroy_dbg test