XLIO Extra API

The information in this chapter is intended for application developers that want to maximize XLIO performance may use the Extra API and achieve the following:

• To further lower latencies

• To increase throughput

• To gain additional CPU cycles for the application logic

• To better control XLIO offload capabilities

All socket applications are limited to the given Socket API interface functions. The XLIO Extra API enables XLIO to open a new set of functions which allow the application developer to add code which utilizes zero copy receive function calls and low-level packet filtering by inspecting the incoming packet headers or packet payload at a very early stage in the processing.

XLIO is designed as a dynamically linked user-space library. As such, the XLIO Extra API has been designed to allow the user to dynamically load XLIO and to detect at runtime if the additional functionality described here is available or not. The application is still able to run over the general socket library without XLIO loaded as it did previously, or can use an application flag to decide which API to use: Socket API or XLIO Extra API.

The XLIO Extra APIs are provided as a header with the XLIO binary rpm. The application developer needs to include this header file in his application code.

After installing the XLIO rpm on the target host, the XLIO Extra APIs header file is located in the following link:

            

            
#include "/usr/include/mellanox/xlio_extra.h"
        

The xlio_extra.h provides detailed information about the various functions and structures, and instructions on how to use them.

An example using the XLIO Extra API can be seen in the udp_lat source code:

• Follow the ‘--xliorxfiltercb’ flag for the packet filter logic

• Follow the ‘--xliozcopyread’ flag for the zero copy recvfrom logic

A specific example for using the TCP zero copy extra API can be seen under extra_api_tests/tcp_zcopy_cb.

During runtime, use the xlio_get_api() function to check if XLIO is loaded in your application and if XLIO Extra API is accessible.

If the function returns with NULL, either XLIO is not loaded with the application, or the XLIO Extra API is not compatible with the header function used for compiling your application. NULL will be the typical return value when running the application on native OS without XLIO loaded. On success the function returns a valid api() pointer and NULL on failure.

Any non-NULL return value is a xlio_api_t type structure pointer that holds pointers to the specific XLIO Extra API function calls which are needed for the application to use. Available functions can be checked using special bit mask field as cap_mask.

It is recommended to call xlio_get_api()once on startup, and to use the returned pointer throughout the life of the process.

There is no need to ‘release’ this pointer in any way.

Adding libxlio.conf Rules During Run-Time

Adds a libxlio.conf rule to the top of the list. This rule will not apply to existing sockets which already considered the conf rules. (around connect/listen/send/recv ..)

Syntax:

            

            
int (*add_conf_rule)(char *config_line);
        

Return value:

• 0 on success

• error code on failure

Where:

• config_line

  • Description – new rule to add to the top of the list (highest priority)

  • Value – a char buffer with the exact format as defined in libxlio.conf, and should end with '\0'

Creating Sockets as Offloaded or Not-Offloaded

Creates sockets on pthread tid as off-loaded/not-off-loaded. This does not affect existing sockets. Offloaded sockets are still subject to libxlio.conf rules.

Usually combined with the XLIO_OFFLOADED_SOCKETS parameter.

Syntax:

            

            
int (*thread_offload)(int offload, pthread_t tid);
        

Return value:

• 0 on success

• error code on failure

Where:

• offload

  • Description – Offload property

  • Value – 1 for offloaded, 0 for not-offloaded

• tid

  • Description – thread ID

The packet filter logic gives the application developer the capability to inspect a received packet. You can then decide, on the fly, to keep or drop the received packet at this stage in processing.

The user’s application packet filtering callback is defined by the prototype:

            

            
typedef xlio_recv_callback_retval_t (*xlio_recv_callback_t) (int fd, size_t sz_iov, struct iovec iov[], struct xlio_info_t* xlio_info, void *context);
        

This callback function should be registered with XLIO by calling the XLIO Extra API function register_recv_callback(). It can be unregistered by setting a NULL function pointer.

XLIO calls the callback to notify of new incoming packets after the internal IP & UDP/TCP header processing, and before they are queued in the socket's receive queue.

The context of the callback is always that of one of the user's application threads that called one of the following socket APIs: select(), poll(), epoll_wait(), recv(), recvfrom(), recvmsg(), read(), or readv().

Zero Copy recvfrom()

Zero-copy recvfrom implementation. This function attempts to receive a packet without doing data copy.

Syntax:

            

            
int (*recvfrom_zcopy)(int s, void *buf, size_t len, int *flags, struct sockaddr *from, socklen_t *fromlen);
        

Where:

The flags parameter can contain the usual flags to recvmsg(), and also the MSG_XLIO_ZCOPY_FORCE flag. If the latter is not set, the function reverts to data copy (i.e., zero-copy cannot be performed). If zero-copy is performed, the flag MSG_XLIO_ZCOPY is set upon exit.

If zero copy is performed (MSG_XLIO_ZCOPY flag is returned), the buffer is filled with a xlio_recvfrom_zcopy_packets_t structure holding as much fragments as `len' allows. The total size of all fragments is returned. Otherwise, the buffer is filled with actual data, and its size is returned (same as recvfrom()).

If the return value is positive, data copy has been performed. If the return value is zero, no data has been received.

Freeing Zero Copied Packet Buffers

Frees a packet received by "recvfrom_zcopy()" or held by "receive callback".

Syntax:

            

            
int (*recvfrom_zcopy_free_packets)(int s, struct xlio_recvfrom_zcopy_packet_t  *pkts , size_t count);
        

Where:

• s – socket from which the packet was received

• pkts – array of packet identifiers

• count – number of packets in the array

Return value:

• 0 on success, -1 on failure

• errno is set to:

  • EINVAL – not a offloaded socket

  • ENOENT – the packet was not received from 's'.

Example:

            

            
entry Source Source-mask Dest Dest-mask Interface Service Routing Status Log |------|------------|---------------|-----|----------|- 1 any any any any if0 any tunneling active 1 2 192.168.2.0 255.255..255.0 any any if1 any tunneling active 1
        

Expected result:

            

            
sRB-20210G-61f0(statistic)# log show counter tx total pack tx total byte rx total pack rx total byte |------|-------------|-------------|-------------|-------------- 1 2733553 268066596 3698 362404
        

Dumps statistics for fd number using log_level log level.

Syntax:

            

            
int (*dump_fd_stats) (int fd, int log_level);
        

Parameters:

For output example see section Monitoring – the xlio_stats Utility. Return values: 0 on success, -1 on failure

The “Dummy Send” feature gives the application developer the capability to send dummy packets in order to warm up the CPU caches on XLIO send path, hence minimizing any cache misses and improving latency. The dummy packets reaches the hardware NIC and then is dropped.

The application developer is responsible for sending the dummy packets by setting the XLIO_SND_FLAGS_DUMMY bit in the flags parameter of send(), sendto(), sendmsg(), and sendmmsg() sockets API.

Parameters:

Same as the original APIs for offloaded sockets. Otherwise, -1 is returned and errno is set to EINVAL.Return values:

Usage example:

            

            
void dummyWait(Timer waitDuration, Timer dummySendCycleDuration) { Timer now = Timer::now(); Timer endTime = now + waitDuration; Timer nextDummySendTime = now + dummySendCycleDuration; for ( ; now < endTime ; now = Timer::now()) { if (now >= nextDummySendTime) { send(fd, buf, len, XLIO_SND_FLAGS_DUMMY); nextDummySendTime += dummySendCycleDuration; } } }
        

This sample code consistently sends dummy packets every DummysendCycleDuration using the XLIO extra API while the total time does not exceed waitDuration.

Verifying “Dummy Send” capability in HW

In order to verify “Dummy Send” capability in the hardware, run XLIO with DEBUG trace level.

            

            
XLIO_TRACELEVEL=DEBUG LD_PRELOAD=<path to libxlio.so> <command line>
        

Look in the printout for “HW Dummy send support for QP = [0|1]”.

For example:

            

            
Pid: 3832 Tid: 3832 XLIO DEBUG: qpm[0x2097310]:121:configure() Creating QP of transport type 'ETH' on ibv device 'mlx5_0' [0x201e460] on port 1 Pid: 3832 Tid: 3832 XLIO DEBUG: qpm[0x2097310]:137:configure() HW Dummy send support for QP = 1 Pid: 3832 Tid: 3832 XLIO DEBUG: cqm[0x203a460]:269:cq_mgr() Created CQ as Tx with fd[25] and of size 3000 elements (ibv_cq_hndl=0x20a0000)
        

“Dummy Packets” Statistics

Run xlio_stats tool to view the total amount of dummy-packets sent.

            

            
xlio_stats –p <pid> -v 3
        

The number of dummy messages sent will appear under the relevant fd. For example:

            

            
====================================================== Fd=[20] - UDP, Blocked, MC Loop Enabled - Local Address = [0.0.0.0:56732] Tx Offload: 128 / 9413 / 0 / 0 [kilobytes/packets/drops/errors] Tx Dummy messages : 87798 Rx Offload: 128 / 9413 / 0 / 0 [kilobytes/packets/eagains/errors] Rx byte: cur 0 / max 14 / dropped 0 / limit 212992 Rx pkt : cur 0 / max 1 / dropped 0 Rx poll: 0 / 9411 (100.00%) [miss/hit] ======================================================
        

The API introduced for this capability allows an application to remove the overhead of socket API from the receive flow data path, while keeping the well-known socket API for the control interface. Using such functionality the application has almost direct access to XLIO’s HW ring object and it is possible to implement a design which does not call socket APIs such as select(), poll(), epoll_wait(), recv(), recvfrom(), recvmsg(), read(), or readv().

The structures and constants are defined as shown below.

XLIO Specific Events

            

            
typedef enum {
    XLIO_SOCKETXTREME_PACKET = (1ULL << 32),
    XLIO_SOCKETXTREME_NEW_CONNECTION_ACCEPTED = (1ULL << 33)
}
xlio_socketxtreme_events_t;
        

XLIO Buffer

            

            
struct xlio_buff_t {
    struct xlio_buff_t* next;
    void* payload;
    uint16_t len;
};
        

            

            
struct xlio_packet_desc_t {
    size_t num_bufs;
    uint16_t total_len;
    struct xlio_buff_t* buff_lst;
};
        

XLIO Packet

            

            
struct xlio_socketxtreme_completion_t {
struct xlio_socketxtreme_packet_desc_t packet;
uint64_t events;
uint64_t user_data;
struct sockaddr_in src;
int listen_fd;
};
        

Polling for XLIO Completions

Syntax:

            

            
int (*socketxtreme_poll)(int fd, struct xlio_socketxtreme_completion_t* completions, unsigned int ncompletions, int flags);
        

Where

• fd – file descriptor

• completions – array of completion elements

• ncompletions – number of elements in passed array

• flags – flags to control behavior (set zero)

Return values: Returns the number of ready completions during success. A negative value is returned in case of failure.

Description: This function polls the `fd` for XLIO completions and returns maximum `ncompletions` - ready completions via the `completions` array. The `fd` represents a ring file descriptor. XLIO completions are indicated for incoming packets and/or for other events. If XLIO_SOCKETXTREME_PACKET flag is enabled in the xlio_socketxtreme_completion_t.events field the completion points to the incoming packet descriptor that can be accessed via the xlio_socketxtreme_completion_t.packet field. Packet descriptor points to the XLIO buffers that contain data scattered by HW, so the data is delivered to the application with zero copy. Notice: after the application is finished with the returned packets and their buffers it must free them using socketxtreme_free_packets ()/socketxtreme_free_buff () functions. If XLIO_SOCKETXTREME_PACKET flag is disabled xlio_socketxtreme_packet_desc_t.packet field is reserved. In addition to packet arrival event (indicated by XLIO_SOCKETXTREME_PACKET flag) XLIO also reports XLIO_SOCKETXTREME_NEW_CONNECTION_ACCEPTED event and standard epoll events via the xlio_socketxtreme_packet_desc_t.events field. XLIO_SOCKETXTREME_NEW_CONNECTION_ACCEPTED event is reported when new connection is accepted by the server. When working with socketxtreme_poll() new connections are accepted automatically and accept (listen_socket) must not be called. XLIO_SOCKETXTREME_NEW_CONNECTION_ACCEPTED event is reported for the new connected/child socket (xlio_socketxtreme_packet_desc_t.user_data refers to child socket) and EPOLLIN event is not generated for the listen socket. For events other than packet arrival and new connection acceptance xlio_socketxtreme_packet_desc_t.events bitmask composed using standard epoll API events types. Notice: the same completion can report multiple events, for example XLIO_SOCKETXTREME_PACKET flag can be enabled together with EPOLLOUT event, etc.

Getting Number of Attached Rings

Syntax:

            

            
int (*get_socket_rings_num)(int fd);
        

Where:

• fd – file descriptor

Return values: Returns the number of rings during success. A negative value is returned in case of failure.

Description: Returns the number of rings that are associated with socket.

Getting Ring FD

Syntax:

            

            
int (*get_socket_rings_fds)(int fd, int *ring_fds, int ring_fds_sz);
        

Where:

• fd – file descriptor

• ring_fds – int array of ring fds

• ring_fds_sz – size of the array

Return values: Returns the number of populated array entries during success. A negative value is returned in case of failure.

Description: Returns FDs of the rings that are associated with the socket.

Free SocketXtreme XLIO Packets

Syntax:

            

            
int (*socketxtreme_free_packets)(struct xlio_socketxtreme_packet_desc_t *packets, int num);
        

Where:

• packets – packets to be freed

• num – number of packets in passed array

Return values: Returns zero value during success. A negative value is returned in case failure.

Description: Frees packets received by socketxtreme_poll().

For each packet in the `packets` array this function updates the receive queue size and the advertised TCP window size, if needed, for the socket that received the packet and frees XLIO buffer list that is associated with the packet. Notice: for each buffer in the buffer list XLIO decreases buffer's ref count and only buffers with ref count zero are deallocated. An application can call socketxtreme_ref_buf() to increase the buffer reference count in order to hold the buffer even after socketxtreme_free_ packets() has been called. Also, the application is responsible to free buffers that could not be deallocated during socketxtreme_free_packets() due to non-zero reference count. This is done by calling the socketxtreme_free_buff() function.

Decrement SocketXtreme XLIO Buffer Reference Counter

Syntax:

            

            
int (*socketxtreme_free_buff)(struct xlio_buff_t *buff);
        

Return values: Returns the buffer's reference count after the change (zero value means that the buffer has been deallocated). A negative value is returned in case of failure.

Description: Decrement the reference counter of a buffer received by socketxtreme_poll(). This function decrements the buff reference count. When buff's reference count reaches zero, it is deallocated.

Increment SocketXtreme XLIO Buffer Reference Counter

Syntax:

            

            
int (*socketxtreme_ref_buff)(struct xlio_buff_t *buff);
        

Where:

• buff – buffer to be managed

Return values: Returns buffer's reference count after the change. A negative value is returned in case of failure.

Description: Increment the reference counter of a buffer received by socketxtreme_poll(). This function increments the reference count of the buffer. This function should be used in order to hold the buffer even after a call to socketxtreme_free_packets(). When the buffer is no longer required it should be freed via socketxtreme_free_buff ().

Usage Example

Sockperf benchmark supports socketxtreme mode. Its source code can be used as a reference of socketxtreme API usage.

The following sample implements server side logic based on the API described above.

In this example, the application just waits for connection requests and accepts new connections.

            

            
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <mellanox/xlio_extra.h>
int main(int argc, char**argv)
{
     int rc = 0;
     int fd = -1;
     struct sockaddr_in addr;
     static struct xlio_api_t *_xlio_api = NULL;
     static int _xlio_ring_fd = -1;
     char *strdev = (argc > 1 ? argv[1] : NULL);
     char *straddr = (argc > 2 ? argv[2] : NULL);
     char *strport = (argc > 3 ? argv[3] : NULL);
    if (!strdev || !straddr || !strport) {
          printf("Wrong options\n");
          exit(1);
     }
     printf("Dev: %s\nAddress: %s\nPort:%s\n", strdev, straddr, strport);
     _/* Get XLIO extra API reference */
     _xlio_api = xlio_get_api();
     if (_xlio_api == NULL) {
          printf("Extra API not found\n");
          exit(1);
     }
     fd = socket(AF_INET, SOCK_STREAM, IPPROTO_IP);
     rc = setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE,
                    (void *)strdev, strlen(strdev));
     if (rc < 0) {
         printf("setsockopt() failed %d : %s\n", errno, strerror(errno));
         exit(1);
     }
     bzero(&addr, sizeof(addr));
     addr.sin_family = AF_INET;
     addr.sin_addr.s_addr = inet_addr(straddr);
     addr.sin_port = htons(atoi(strport));
     rc = bind(fd, (struct sockaddr *)&addr, sizeof(addr));
     if (rc < 0) {
          fprintf(stderr, "bind() failed %d : %s\n", errno, strerror(errno));
          exit(1);
     }
     listen(fd, 5);
     printf("Waiting on: fd=%d\n", fd);
     _/* RX ring is available after listen() */
     _xlio_api->get_socket_rings_fds(fd, &_xlio_ring_fd, 1);
     if (_xlio_ring_fd == -1){
          printf("Failed to return the ring fd\n");
          exit(1);
     }
     while (0 == rc) {
         struct xlio_socketxtreme_completion_t xlio_comps;
         /* Polling any RX events / data */
         rc = _xlio_api->socketxtreme_poll(_xlio_ring_fd, &xlio_comps, 1, 0);
         if (rc > 0) {
             printf("socketxtreme_poll: rc=%d event=0x%lx user_data=%ld\n",
                 rc, xlio_comps.events, xlio_comps.user_data);
             if (xlio_comps.events & XLIO_SOCKETXTREME_NEW_CONNECTION_ACCEPTED) {
                 printf("Accepted connection: fd=%d\n", (int)xlio_comps.user_data);
                 rc = 0;
             }
         }
     }
     close(fd);
     fprintf(stderr, "socket closed\n");
     return 0;
        

Limitations

No support for:

• Multi-thread

User should keep in mind the differences in flow between the standard socket API and that based on the polling completions model.

• SocketXtreme mode is used with non-blocking connect() call only

• Do not use accept() because socketxtreme_poll() provides special event as XLIO_socketxtreme_NEW_CONNECTION_ACCEPTED to track connection request

• Mixed receive methods (recv/recvfrom/recmsg/epoll_wait with socketXtreme) can cause the user to receive out-of-order packets. UDP is an unreliable protocol, hence working with mixed receive methods are allowed yet not recommended. Whereas TCP is a reliable protocol, hence mixed receive methods are not allowed. socketxtreme_poll() is able to notify about any received data using the event XLIO_socketxtreme_PACKET.

This function allows to communicate with library using extendable protocol

based on struct cmshdr.

Syntax:

            

            
int (*ioctl) (void *cmsg_hdr, size_t cmsg_len);
        

Parameters:

The cmsg_hdr parameter points to the ancillary data. This cmsg_hdr pointer points to the following structure (C/C++ example shown) that describes the ancillary data.

            

            
struct cmsghdr {
    size_t   cmsg_len;       /* data byte count includes hdr */
    int      cmsg_level;     /* originating protocol         */
    int      cmsg_type;      /* protocol-specific type       */
    /* followed by u_char    cmsg_data[]; */
   };
        

Ancillary data is a sequence of cmsghdr structures with appended data. The sequence of cmsghdr structures should never be accessed directly. Instead, use only the following macros: CMSG_ALIGN, CMSG_SPACE, CMSG_DATA, CMSG_LEN.

Guidelines:

• The cmsg_len should be set to the length of the cmsghdr plus the length of all ancillary data that follows immediately after the cmsghdr. This is represented by the commented out cmsg_data field.

• The cmsg_level should be set to the option level (for example, SOL_SOCKET).

• The cmsg_type should be set to the option name (for example, CMSG_XLIO_IOCTL_USER_ALLOC).

Supported commands:

CMSG_XLIO_IOCTL_USER_ALLOC

Control Flags

            

            
enum {
    IOCTL_USER_ALLOC_TX = (1 << 0),
    IOCTL_USER_ALLOC_RX = (1 << 1),
    IOCTL_USER_ALLOC_TX_ZC = (1 << 2)
};
        

Usage Example

In this example, the application uses CMSG_XLIO_IOCTL_USER_ALLOC command.

            

            
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <arpa/inet.h>
#include <mellanox/xlio_extra.h>
void * my_alloc(size_t sz_bytes)
{
        void *m_data_block = NULL;
        long page_size = sysconf(_SC_PAGESIZE);
        if (page_size > 0) {
                    sz_bytes = (sz_bytes + page_size - 1) & (~page_size - 1);
                    int ret = posix_memalign(&m_data_block, page_size, sz_bytes);
                    if (!ret) {
                               return NULL;
                    }
        }
        return m_data_block;
}
void my_free(void *ptr)
{
        free(ptr);
}
int main(int argc, char *argv[])
{
    int sockfd = 0, n = 0;
    char recvBuff[1024];
    struct sockaddr_in serv_addr;
    if(argc != 2)
    {
        printf("\n Usage: %s <ip of server> \n",argv[0]);
        return 1;
    }
#pragma pack(push, 1)
    struct {
    uint8_t flags;
    void* (*alloc_func)(size_t);
    void (*free_func)(void *);
    } data;
#pragma pack( pop )
    struct cmsghdr *cmsg;
    char cbuf[CMSG_SPACE(sizeof(data))];
    errno = 0;
    cmsg = (struct cmsghdr *)cbuf;
    cmsg->cmsg_level = SOL_SOCKET;
    cmsg->cmsg_type = CMSG_XLIO_IOCTL_USER_ALLOC;
    cmsg->cmsg_len = CMSG_LEN(sizeof(data));
    data.flags = 0x03;
    data.alloc_func = my_alloc;
    data.free_func = my_free;
    memcpy(CMSG_DATA(cmsg), &data, sizeof(data));
 
    struct xlio_api_t *extra_api;
    extra_api = xlio_get_api();
    printf("extra_api=%p\n", extra_api);
 
    int rc = 0;
    if (extra_api) rc = extra_api->ioctl(cmsg, cmsg->cmsg_len);
    printf("extra_api->ioctl() rc=%d\n");
    memset(recvBuff, '0',sizeof(recvBuff));
    if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    {
        printf("\n Error : Could not create socket \n");
        return 1;
    }
 
    memset(&serv_addr, '0', sizeof(serv_addr));
 
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(5000);
 
    if(inet_pton(AF_INET, argv[1], &serv_addr.sin_addr)<=0)
    {
        printf("\n inet_pton error occured\n");
        return 1;
    }
    if( connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0)
    {
       printf("\n Error : Connect Failed \n");
       return 1;
    }
 
    while ( (n = read(sockfd, recvBuff, sizeof(recvBuff)-1)) > 0)
    {
        recvBuff[n] = 0;
        if(fputs(recvBuff, stdout) == EOF)
        {
            printf("\n Error : Fputs error\n");
        }
    }
 
    if(n < 0)
    {
        printf("\n Read error \n");
    }
 
    return 0;
}