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authorPaolo Bonzini <pbonzini@redhat.com>2015-03-28 07:37:18 +0100
committerKevin Wolf <kwolf@redhat.com>2015-04-28 15:36:09 +0200
commit0b5a24454fc551f0294fe93821e8c643214a55f5 (patch)
tree3c4e764314d8f157a31ebc4903f04161c7a44fb5 /block.c
parenta7282330c01364ef00260749bc6a37c7f16ec047 (diff)
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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>
Diffstat (limited to 'block.c')
-rw-r--r--block.c43
1 files changed, 34 insertions, 9 deletions
diff --git a/block.c b/block.c
index 70aed80..d13b2e7 100644
--- a/block.c
+++ b/block.c
@@ -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;
}