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block: avoid unnecessary bottom halves 

bdrv_aio_* APIs can use coroutines to achieve asynchronicity.  However,
the coroutine may terminate without having yielded back to the caller
(for example because of something that invokes a nested event loop,
or because the coroutine is doing nothing at all).  In this case,
the bdrv_aio_* API must delay the completion to the next iteration
of the main loop, because bdrv_aio_* will never invoke the callback
before returning.

This can be done with a bottom half, and indeed bdrv_aio_* is always
using one for simplicity.  It is possible to gain some performance
(~3%) by avoiding this in the common case.  A new field in the
BlockAIOCBCoroutine struct is set to true until the first time the
corotine has yielded to its creator, and completion goes through a
new function bdrv_co_complete.  If the flag is false, bdrv_co_complete
invokes the callback immediately.  If it is true, the caller will
notice that the coroutine has completed and schedule the bottom
half itself.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 1427524638-28157-1-git-send-email-pbonzini@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Paolo Bonzini 2015-03-28 07:37:18 +01:00 committed by Kevin Wolf
parent a7282330c0
commit 0b5a24454f
1 changed files with 34 additions and 9 deletions
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43
block.c
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@ -4849,6 +4849,7 @@ typedef struct BlockAIOCBCoroutine {
BlockAIOCB common;
BlockRequest req;
bool is_write;
bool need_bh;
bool *done;
QEMUBH* bh;
} BlockAIOCBCoroutine;
@ -4857,14 +4858,32 @@ static const AIOCBInfo bdrv_em_co_aiocb_info = {
.aiocb_size = sizeof(BlockAIOCBCoroutine),
};
static void bdrv_co_complete(BlockAIOCBCoroutine *acb)
{
if (!acb->need_bh) {
acb->common.cb(acb->common.opaque, acb->req.error);
qemu_aio_unref(acb);
}
}
static void bdrv_co_em_bh(void *opaque)
{
BlockAIOCBCoroutine *acb = opaque;
acb->common.cb(acb->common.opaque, acb->req.error);
assert(!acb->need_bh);
qemu_bh_delete(acb->bh);
qemu_aio_unref(acb);
bdrv_co_complete(acb);
}
static void bdrv_co_maybe_schedule_bh(BlockAIOCBCoroutine *acb)
{
acb->need_bh = false;
if (acb->req.error != -EINPROGRESS) {
BlockDriverState *bs = acb->common.bs;
acb->bh = aio_bh_new(bdrv_get_aio_context(bs), bdrv_co_em_bh, acb);
qemu_bh_schedule(acb->bh);
}
}
/* Invoke bdrv_co_do_readv/bdrv_co_do_writev */
@ -4881,8 +4900,7 @@ static void coroutine_fn bdrv_co_do_rw(void *opaque)
acb->req.nb_sectors, acb->req.qiov, acb->req.flags);
}
acb->bh = aio_bh_new(bdrv_get_aio_context(bs), bdrv_co_em_bh, acb);
qemu_bh_schedule(acb->bh);
bdrv_co_complete(acb);
}
static BlockAIOCB *bdrv_co_aio_rw_vector(BlockDriverState *bs,
@ -4898,6 +4916,8 @@ static BlockAIOCB *bdrv_co_aio_rw_vector(BlockDriverState *bs,
BlockAIOCBCoroutine *acb;
acb = qemu_aio_get(&bdrv_em_co_aiocb_info, bs, cb, opaque);
acb->need_bh = true;
acb->req.error = -EINPROGRESS;
acb->req.sector = sector_num;
acb->req.nb_sectors = nb_sectors;
acb->req.qiov = qiov;
@ -4907,6 +4927,7 @@ static BlockAIOCB *bdrv_co_aio_rw_vector(BlockDriverState *bs,
co = qemu_coroutine_create(bdrv_co_do_rw);
qemu_coroutine_enter(co, acb);
bdrv_co_maybe_schedule_bh(acb);
return &acb->common;
}
@ -4916,8 +4937,7 @@ static void coroutine_fn bdrv_aio_flush_co_entry(void *opaque)
BlockDriverState *bs = acb->common.bs;
acb->req.error = bdrv_co_flush(bs);
acb->bh = aio_bh_new(bdrv_get_aio_context(bs), bdrv_co_em_bh, acb);
qemu_bh_schedule(acb->bh);
bdrv_co_complete(acb);
}
BlockAIOCB *bdrv_aio_flush(BlockDriverState *bs,
@ -4929,10 +4949,13 @@ BlockAIOCB *bdrv_aio_flush(BlockDriverState *bs,
BlockAIOCBCoroutine *acb;
acb = qemu_aio_get(&bdrv_em_co_aiocb_info, bs, cb, opaque);
acb->need_bh = true;
acb->req.error = -EINPROGRESS;
co = qemu_coroutine_create(bdrv_aio_flush_co_entry);
qemu_coroutine_enter(co, acb);
bdrv_co_maybe_schedule_bh(acb);
return &acb->common;
}
@ -4942,8 +4965,7 @@ static void coroutine_fn bdrv_aio_discard_co_entry(void *opaque)
BlockDriverState *bs = acb->common.bs;
acb->req.error = bdrv_co_discard(bs, acb->req.sector, acb->req.nb_sectors);
acb->bh = aio_bh_new(bdrv_get_aio_context(bs), bdrv_co_em_bh, acb);
qemu_bh_schedule(acb->bh);
bdrv_co_complete(acb);
}
BlockAIOCB *bdrv_aio_discard(BlockDriverState *bs,
@ -4956,11 +4978,14 @@ BlockAIOCB *bdrv_aio_discard(BlockDriverState *bs,
trace_bdrv_aio_discard(bs, sector_num, nb_sectors, opaque);
acb = qemu_aio_get(&bdrv_em_co_aiocb_info, bs, cb, opaque);
acb->need_bh = true;
acb->req.error = -EINPROGRESS;
acb->req.sector = sector_num;
acb->req.nb_sectors = nb_sectors;
co = qemu_coroutine_create(bdrv_aio_discard_co_entry);
qemu_coroutine_enter(co, acb);
bdrv_co_maybe_schedule_bh(acb);
return &acb->common;
}