lkml.org 
[lkml]   [2010]   [May]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    SubjectRe: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself
    Date
    On Thu, 20 May 2010 02:31:50 pm Rusty Russell wrote:
    > On Wed, 19 May 2010 05:36:42 pm Avi Kivity wrote:
    > > > Note that this is a exclusive->shared->exclusive bounce only, too.
    > > >
    > >
    > > A bounce is a bounce.
    >
    > I tried to measure this to show that you were wrong, but I was only able
    > to show that you're right. How annoying. Test code below.

    This time for sure!

    #define _GNU_SOURCE
    #include <unistd.h>
    #include <sched.h>
    #include <err.h>
    #include <stdbool.h>
    #include <stdint.h>
    #include <string.h>
    #include <stdlib.h>
    #include <stdio.h>
    #include <sys/time.h>
    #include <sys/mman.h>

    /* We share memory via an mmap. */
    struct counter {
    unsigned int cacheline1;
    char pad[256];
    unsigned int cacheline2;
    };

    #define MAX_BOUNCES 100000000

    enum mode {
    SHARE,
    UNSHARE,
    LOCKSHARE,
    LOCKUNSHARE,
    };

    int main(int argc, char *argv[])
    {
    cpu_set_t cpuset;
    volatile struct counter *counter;
    struct timeval start, stop;
    bool child;
    unsigned int count;
    uint64_t usec;
    enum mode mode;

    if (argc != 4)
    errx(1, "Usage: cachebounce share|unshare|lockshare|lockunshare <cpu0> <cpu1>");

    if (strcmp(argv[1], "share") == 0)
    mode = SHARE;
    else if (strcmp(argv[1], "unshare") == 0)
    mode = UNSHARE;
    else if (strcmp(argv[1], "lockshare") == 0)
    mode = LOCKSHARE;
    else if (strcmp(argv[1], "lockunshare") == 0)
    mode = LOCKSHARE;
    else
    errx(1, "Usage: cachebounce share|unshare|lockshare|lockunshare <cpu0> <cpu1>");

    CPU_ZERO(&cpuset);

    counter = mmap(NULL, getpagesize(), PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_SHARED, -1, 0);
    if (counter == MAP_FAILED)
    err(1, "Mapping page");

    /* Fault it in. */
    counter->cacheline1 = counter->cacheline2 = 0;

    child = (fork() == 0);

    CPU_SET(atoi(argv[2 + child]), &cpuset);
    if (sched_setaffinity(getpid(), sizeof(cpu_set_t), &cpuset) != 0)
    err(1, "Calling sched_setaffinity()");

    gettimeofday(&start, NULL);

    if (child) {
    count = 1;
    switch (mode) {
    case SHARE:
    while (count < MAX_BOUNCES) {
    /* Spin waiting for other side to change it. */
    while (counter->cacheline1 != count);
    count++;
    counter->cacheline1 = count;
    count++;
    }
    break;
    case UNSHARE:
    while (count < MAX_BOUNCES) {
    /* Spin waiting for other side to change it. */
    while (counter->cacheline1 != count);
    count++;
    counter->cacheline2 = count;
    count++;
    }
    break;
    case LOCKSHARE:
    while (count < MAX_BOUNCES) {
    /* Spin waiting for other side to change it. */
    while (__sync_val_compare_and_swap(&counter->cacheline1, count, count+1)
    != count);
    count += 2;
    }
    break;
    case LOCKUNSHARE:
    while (count < MAX_BOUNCES) {
    /* Spin waiting for other side to change it. */
    while (counter->cacheline1 != count);
    __sync_val_compare_and_swap(&counter->cacheline2, count, count+1);
    count += 2;
    }
    break;
    }
    } else {
    count = 0;
    switch (mode) {
    case SHARE:
    while (count < MAX_BOUNCES) {
    /* Spin waiting for other side to change it. */
    while (counter->cacheline1 != count);
    count++;
    counter->cacheline1 = count;
    count++;
    }
    break;
    case UNSHARE:
    while (count < MAX_BOUNCES) {
    /* Spin waiting for other side to change it. */
    while (counter->cacheline2 != count);
    count++;
    counter->cacheline1 = count;
    count++;
    }
    break;
    case LOCKSHARE:
    while (count < MAX_BOUNCES) {
    /* Spin waiting for other side to change it. */
    while (__sync_val_compare_and_swap(&counter->cacheline1, count, count+1)
    != count);
    count += 2;
    }
    break;
    case LOCKUNSHARE:
    while (count < MAX_BOUNCES) {
    /* Spin waiting for other side to change it. */
    while (counter->cacheline2 != count);
    __sync_val_compare_and_swap(&counter->cacheline1, count, count+1);
    count += 2;
    }
    break;
    }
    }
    gettimeofday(&stop, NULL);
    usec = (stop.tv_sec * 1000000LL + stop.tv_usec)
    - (start.tv_sec * 1000000LL + start.tv_usec);
    printf("CPU %s: %s cacheline: %llu usec\n", argv[2+child], argv[1], usec);
    return 0;
    }



    \
     
     \ /
      Last update: 2010-05-20 07:11    [W:0.026 / U:31.352 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site