Commit 5b8bb359 authored by Paolo Bonzini's avatar Paolo Bonzini Committed by Kevin Wolf
Browse files

async: add aio_bh_schedule_oneshot 



qemu_bh_delete is already clearing bh->scheduled at the same time
as it's setting bh->deleted.  Since it's not using any memory
barriers, there is no synchronization going on for bh->deleted,
and this makes the bh->deleted checks superfluous in aio_compute_timeout,
aio_bh_poll and aio_ctx_check.

Just remove them, and put the (bh->scheduled && bh->deleted) combo
to work in a new function aio_bh_schedule_oneshot.  The new function
removes the need to save the QEMUBH pointer between the creation
and the execution of the bottom half.

Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
parent 818bbc86

async.c

+23 −4
Original line number Diff line number Diff line
@@ -44,6 +44,25 @@ struct QEMUBH { 
    bool deleted;

};



void aio_bh_schedule_oneshot(AioContext *ctx, QEMUBHFunc *cb, void *opaque)

{

    QEMUBH *bh;

    bh = g_new(QEMUBH, 1);

    *bh = (QEMUBH){

        .ctx = ctx,

        .cb = cb,

        .opaque = opaque,

    };

    qemu_mutex_lock(&ctx->bh_lock);

    bh->next = ctx->first_bh;

    bh->scheduled = 1;

    bh->deleted = 1;

    /* Make sure that the members are ready before putting bh into list */

    smp_wmb();

    ctx->first_bh = bh;

    qemu_mutex_unlock(&ctx->bh_lock);

}



QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque)

{

    QEMUBH *bh;
@@ -86,7 +105,7 @@ int aio_bh_poll(AioContext *ctx) 
         * thread sees the zero before bh->cb has run, and thus will call

         * aio_notify again if necessary.

         */

        if (!bh->deleted && atomic_xchg(&bh->scheduled, 0)) {

        if (atomic_xchg(&bh->scheduled, 0)) {

            /* Idle BHs and the notify BH don't count as progress */

            if (!bh->idle && bh != ctx->notify_dummy_bh) {

                ret = 1;
@@ -104,7 +123,7 @@ int aio_bh_poll(AioContext *ctx) 
        bhp = &ctx->first_bh;

        while (*bhp) {

            bh = *bhp;

            if (bh->deleted) {

            if (bh->deleted && !bh->scheduled) {

                *bhp = bh->next;

                g_free(bh);

            } else {
@@ -168,7 +187,7 @@ aio_compute_timeout(AioContext *ctx) 
    QEMUBH *bh;



    for (bh = ctx->first_bh; bh; bh = bh->next) {

        if (!bh->deleted && bh->scheduled) {

        if (bh->scheduled) {

            if (bh->idle) {

                /* idle bottom halves will be polled at least

                 * every 10ms */
@@ -216,7 +235,7 @@ aio_ctx_check(GSource *source) 
    aio_notify_accept(ctx);



    for (bh = ctx->first_bh; bh; bh = bh->next) {

        if (!bh->deleted && bh->scheduled) {

        if (bh->scheduled) {

            return true;

        }

    }

include/block/aio.h

+6 −0
Original line number Diff line number Diff line
@@ -180,6 +180,12 @@ void aio_context_acquire(AioContext *ctx); 
/* Relinquish ownership of the AioContext. */

void aio_context_release(AioContext *ctx);



/**

 * aio_bh_schedule_oneshot: Allocate a new bottom half structure that will run

 * only once and as soon as possible.

 */

void aio_bh_schedule_oneshot(AioContext *ctx, QEMUBHFunc *cb, void *opaque);



/**

 * aio_bh_new: Allocate a new bottom half structure.

 *