From 0706d1c4cad581d9f213e742a518be939b05a733 Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Fri, 22 Apr 2016 10:09:35 +0200 Subject: [PATCH 5/5] virtio-blk: use blk_io_plug/unplug for Linux AIO batching RH-Author: Stefan Hajnoczi Message-id: <1461319775-24446-2-git-send-email-stefanha@redhat.com> Patchwork-id: 70224 O-Subject: [RHEV-7.2.z qemu-kvm-rhev PATCH 1/1] virtio-blk: use blk_io_plug/unplug for Linux AIO batching Bugzilla: 1327613 RH-Acked-by: Laurent Vivier RH-Acked-by: Fam Zheng RH-Acked-by: Kevin Wolf The raw-posix block driver implements Linux AIO batching so multiple requests can be submitted with a single io_submit(2) system call. Batching is currently only used by virtio-scsi and virtio-blk-data-plane. Enable batching for regular virtio-blk so the number of io_submit(2) system calls is reduced for workloads with queue depth > 1. In 4KB random read performance tests with queue depth 32, the CPU utilization on the host is reduced by 9.4%. The fio job is as follows: [global] bs=4k ioengine=libaio iodepth=32 direct=1 sync=0 time_based=1 runtime=30 clocksource=gettimeofday ramp_time=5 [job1] rw=randread filename=/dev/vdb size=4096M write_bw_log=fio write_iops_log=fio write_lat_log=fio log_avg_msec=1000 This benchmark was run on an raw image on LVM. The disk was an SSD drive and -drive cache=none,aio=native was used. Tested-by: Pradeep Surisetty Signed-off-by: Stefan Hajnoczi Reviewed-by: Fam Zheng (cherry-picked from commit fc73548e444ae3239f6cef44a5200b5d2c3e85d1) Signed-off-by: Stefan Hajnoczi Signed-off-by: Miroslav Rezanina --- hw/block/virtio-blk.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c index 6dd7fed..c99aefd 100644 --- a/hw/block/virtio-blk.c +++ b/hw/block/virtio-blk.c @@ -604,6 +604,8 @@ static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq) return; } + blk_io_plug(s->blk); + while ((req = virtio_blk_get_request(s))) { virtio_blk_handle_request(req, &mrb); } @@ -611,6 +613,8 @@ static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq) if (mrb.num_reqs) { virtio_blk_submit_multireq(s->blk, &mrb); } + + blk_io_unplug(s->blk); } static void virtio_blk_dma_restart_bh(void *opaque) -- 1.8.3.1