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dataplane: submit I/O as a batch

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Before commit 580b6b2aa2(dataplane: use the QEMU block
layer for I/O), dataplane for virtio-blk submits block
I/O as a batch.

This commit 580b6b2aa2 replaces the custom linux AIO
implementation(including submit I/O as a batch) with QEMU
block layer, but this commit causes ~40% throughput regression
on virtio-blk performance, and removing submitting I/O
as a batch is one of the causes.

This patch applies the newly introduced bdrv_io_plug() and
bdrv_io_unplug() interfaces to support submitting I/O
at batch for Qemu block layer, and in my test, the change
can improve throughput by ~30% with 'aio=native'.

Following my fio test script:

	[global]
	direct=1
	size=4G
	bsrange=4k-4k
	timeout=40
	numjobs=4
	ioengine=libaio
	iodepth=64
	filename=/dev/vdc
	group_reporting=1

	[f]
	rw=randread

Result on one of my small machine(host: x86_64, 2cores, 4thread, guest: 4cores):
	- qemu master: 65K IOPS
	- qemu master with these patches: 92K IOPS
	- 2.0.0 release(dataplane using custom linux aio): 104K IOPS

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Ming Lei 2014-07-04 18:04:35 +08:00 committed by Stefan Hajnoczi
parent 1b3abdcccf
commit dd67c1d7e7
1 changed files with 2 additions and 0 deletions
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2
hw/block/dataplane/virtio-blk.c
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@ -84,6 +84,7 @@ static void handle_notify(EventNotifier *e)
};
event_notifier_test_and_clear(&s->host_notifier);
bdrv_io_plug(s->blk->conf.bs);
for (;;) {
/* Disable guest->host notifies to avoid unnecessary vmexits */
vring_disable_notification(s->vdev, &s->vring);
@ -117,6 +118,7 @@ static void handle_notify(EventNotifier *e)
break;
}
}
bdrv_io_unplug(s->blk->conf.bs);
}
/* Context: QEMU global mutex held */