source: example/io/batch-readv.c@ 012cfc3

// Program to test the optimial batchsize in a single threaded process
extern "C" {
        #include <getopt.h>
        #include <locale.h>
        #include <time.h>                                                                               // timespec
        #include <sys/time.h>                                                                   // timeval
}

enum { TIMEGRAN = 1000000000LL };                                       // nanosecond granularity, except for timeval

#include <omp.h>

#include "io_uring.h"


int myfd;

long long unsigned submits   = 0;
long long unsigned completes = 0;

void submit_and_drain(struct iovec * iov, int n) {
        for(int i = 0; i < n; i++) {
                struct io_uring_sqe * sqe =  &self.io.submit_q.sqes[ 0 ];

                sqe->opcode = IORING_OP_READV;
                #if !defined(IOSQE_ASYNC)
                        sqe->flags = 0;
                #else
                        sqe->flags = IOSQE_ASYNC;
                #endif
                sqe->ioprio = 0;
                sqe->fd = myfd;
                sqe->off = 0;
                sqe->addr = (__u64)iov;
                sqe->len = 1;
                sqe->rw_flags = 0;
                sqe->__pad2[0] = sqe->__pad2[1] = sqe->__pad2[2] = 0;
        }

        volatile uint32_t * tail = self.io.submit_q.tail;
        __atomic_fetch_add(tail, n, __ATOMIC_SEQ_CST);

        int ret = syscall( __NR_io_uring_enter, self.io.fd, n, n, IORING_ENTER_GETEVENTS, nullptr, 0);
        if( ret < 0 ) {
                switch((int)errno) {
                case EAGAIN:
                case EINTR:
                default:
                        fprintf(stderr, "KERNEL ERROR: IO_URING WAIT - %s\n", strerror(errno) );
                        abort();
                }
        }

        submits += ret;

        uint32_t chead = *self.io.completion_q.head;
        uint32_t ctail = *self.io.completion_q.tail;
        const uint32_t mask = *self.io.completion_q.mask;

        // Memory barrier
        __atomic_thread_fence( __ATOMIC_SEQ_CST );

        uint32_t count = ctail - chead;
        __atomic_fetch_add( self.io.completion_q.head, count, __ATOMIC_RELAXED );
        completes += count;
}

uint64_t timeHiRes() {
        timespec curr;
        clock_gettime( CLOCK_REALTIME, &curr );
        return (int64_t)curr.tv_sec * TIMEGRAN + curr.tv_nsec;
}

uint64_t to_miliseconds( uint64_t durtn ) { return durtn / (TIMEGRAN / 1000LL); }
double to_fseconds(uint64_t durtn ) { return durtn / (double)TIMEGRAN; }
uint64_t from_fseconds(double sec) { return sec * TIMEGRAN; }

int main(int argc, char * argv[]) {
        int buflen = 50;
        int batch  = 1;
        double duration = 5;

        setlocale(LC_ALL, "");

        for(;;) {
                static struct option options[] = {
                        {"duration",     required_argument, 0, 'd'},
                        {"batchsize",   required_argument, 0, 'b'},
                        {"buflen",      required_argument, 0, 'l'},
                        {0, 0, 0, 0}
                };

                int idx = 0;
                int opt = getopt_long(argc, argv, "d:l:b:", options, &idx);

                const char * arg = optarg ? optarg : "";
                char * end;
                switch(opt) {
                        // Exit Case
                        case -1:
                                goto arg_loop;
                        case 'd': \
                                duration = strtod(arg, &end); \
                                if(*end != '\0') { \
                                        fprintf(stderr, "Duration must be a valid double, was %s\n", arg); \
                                        goto usage; \
                                } \
                                break;
                        case 'l':
                                buflen = strtoul(arg, &end, 10);
                                if(*end != '\0' && buflen < 10) {
                                        fprintf(stderr, "Buffer size must be at least 10, was %s\n", arg);
                                        goto usage;
                                }
                        case 'b':
                                batch = strtoul(arg, &end, 10);
                                if(*end != '\0' && batch < 0) {
                                        fprintf(stderr, "Batch size must be at least 1, was %s\n", arg);
                                        goto usage;
                                }
                                break;
                        default: /* ? */
                                fprintf(stderr, "%d\n", opt);
                        usage:
                                fprintf( stderr, "  -l, --buflen=SIZE        Number of bytes to read per request\n" );
                                fprintf( stderr, "  -b, --batchsize=COUNT    Number of request to batch together\n" );
                                exit(EXIT_FAILURE);
                }
        }
        arg_loop:

        myfd = open(__FILE__, 0);

        init_uring(2048);

        // Allocate the sqe
        uint32_t idx = 0;

        // Return the sqe
        struct io_uring_sqe * sqe =  &self.io.submit_q.sqes[ idx & (*self.io.submit_q.mask)];

        char data[buflen];
        struct iovec iov = { data, (size_t)buflen };

        sqe->opcode = IORING_OP_READV;
        #if !defined(IOSQE_ASYNC)
                sqe->flags = 0;
        #else
                sqe->flags = IOSQE_ASYNC;
        #endif
        sqe->ioprio = 0;
        sqe->fd = myfd;
        sqe->off = 0;
        sqe->addr = (__u64)&iov;
        sqe->len = 1;
        sqe->rw_flags = 0;
        sqe->__pad2[0] = sqe->__pad2[1] = sqe->__pad2[2] = 0;

        // Append to the list of ready entries
        for(unsigned i = 0; i < *self.io.submit_q.num; i++) {
                self.io.submit_q.array[ i ] = 0;
        }

        printf("Running for %f second, reading %d bytes in batches of %d\n", duration, buflen, batch);
        uint64_t start = timeHiRes();
        uint64_t end   = timeHiRes();
        uint64_t prev  = timeHiRes();
        for(;;) {
                submit_and_drain(&iov, batch);
                end = timeHiRes();
                uint64_t delta = end - start;
                if( to_fseconds(end - prev) > 0.1 ) {
                        printf(" %.1f\r", to_fseconds(delta));
                        fflush(stdout);
                        prev = end;
                }
                if( delta >= from_fseconds(duration) ) {
                        break;
                }
        }

        printf("Took %'ld ms\n", to_miliseconds(end - start));
        printf("Submitted        %'llu\n", submits);
        printf("Completed        %'llu\n", completes);
        printf("Submitted / sec  %'.f\n", submits   / to_fseconds(end - start));
        printf("Completed / sec  %'.f\n", completes / to_fseconds(end - start));
        printf("ns per Submitted %'.f\n", 1000000000.0 * to_fseconds(end - start) / (submits   / batch) );
        printf("ns per Completed %'.f\n", 1000000000.0 * to_fseconds(end - start) / (completes / batch) );
}