From dd67c1d7e75151e2c058ccdd2162643074357442 Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Fri, 4 Jul 2014 18:04:35 +0800 Subject: [PATCH] dataplane: submit I/O as a batch 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 Signed-off-by: Ming Lei Signed-off-by: Stefan Hajnoczi --- hw/block/dataplane/virtio-blk.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c index 4c5ba18122..4bc0729bf7 100644 --- a/hw/block/dataplane/virtio-blk.c +++ b/hw/block/dataplane/virtio-blk.c @@ -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 */