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async: add aio_bh_schedule_oneshot

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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: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Paolo Bonzini 2016-10-03 18:14:15 +02:00 committed by Kevin Wolf
parent 818bbc86c9
commit 5b8bb3595a
2 changed files with 29 additions and 4 deletions
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27
async.c
View File

@ -44,6 +44,25 @@ struct QEMUBH {
bool deleted; 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 *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
{ {
QEMUBH *bh; 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 * thread sees the zero before bh->cb has run, and thus will call
* aio_notify again if necessary. * 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 */ /* Idle BHs and the notify BH don't count as progress */
if (!bh->idle && bh != ctx->notify_dummy_bh) { if (!bh->idle && bh != ctx->notify_dummy_bh) {
ret = 1; ret = 1;
@ -104,7 +123,7 @@ int aio_bh_poll(AioContext *ctx)
bhp = &ctx->first_bh; bhp = &ctx->first_bh;
while (*bhp) { while (*bhp) {
bh = *bhp; bh = *bhp;
if (bh->deleted) { if (bh->deleted && !bh->scheduled) {
*bhp = bh->next; *bhp = bh->next;
g_free(bh); g_free(bh);
} else { } else {
@ -168,7 +187,7 @@ aio_compute_timeout(AioContext *ctx)
QEMUBH *bh; QEMUBH *bh;
for (bh = ctx->first_bh; bh; bh = bh->next) { for (bh = ctx->first_bh; bh; bh = bh->next) {
if (!bh->deleted && bh->scheduled) { if (bh->scheduled) {
if (bh->idle) { if (bh->idle) {
/* idle bottom halves will be polled at least /* idle bottom halves will be polled at least
* every 10ms */ * every 10ms */
@ -216,7 +235,7 @@ aio_ctx_check(GSource *source)
aio_notify_accept(ctx); aio_notify_accept(ctx);
for (bh = ctx->first_bh; bh; bh = bh->next) { for (bh = ctx->first_bh; bh; bh = bh->next) {
if (!bh->deleted && bh->scheduled) { if (bh->scheduled) {
return true; return true;
} }
} }

6
include/block/aio.h
View File

@ -180,6 +180,12 @@ void aio_context_acquire(AioContext *ctx);
/* Relinquish ownership of the AioContext. */ /* Relinquish ownership of the AioContext. */
void aio_context_release(AioContext *ctx); 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. * aio_bh_new: Allocate a new bottom half structure.
* *