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[Qemu-devel] [PATCH] block: avoid unnecessary bottom halves
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PATCH] block: avoid unnecessary bottom halves |
Date: |
Sat, 28 Mar 2015 07:37:18 +0100 |
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 <address@hidden>
---
block.c | 43 ++++++++++++++++++++++++++++++++++---------
1 file changed, 34 insertions(+), 9 deletions(-)
diff --git a/block.c b/block.c
index 0fe97de..3fe0642 100644
--- a/block.c
+++ b/block.c
@@ -4789,6 +4789,7 @@ typedef struct BlockAIOCBCoroutine {
BlockAIOCB common;
BlockRequest req;
bool is_write;
+ bool need_bh;
bool *done;
QEMUBH* bh;
} BlockAIOCBCoroutine;
@@ -4797,14 +4798,32 @@ 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 */
@@ -4821,8 +4840,7 @@ 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,
@@ -4838,6 +4856,8 @@ 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;
@@ -4847,6 +4867,7 @@ 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;
}
@@ -4856,8 +4877,7 @@ 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,
@@ -4869,10 +4889,13 @@ 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;
}
@@ -4882,8 +4905,7 @@ 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,
@@ -4896,11 +4918,14 @@ 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;
}
--
2.3.4
- [Qemu-devel] [PATCH] block: avoid unnecessary bottom halves,
Paolo Bonzini <=