On 09/25/2012 10:36 AM, Asias He wrote:
> This reduces unnecessary interrupts that host could send to guest while
> guest is in the progress of irq handling.
>
> If one vcpu is handling the irq, while another interrupt comes, in
> handle_edge_irq(), the guest will mask the interrupt via mask_msi_irq()
> which is a very heavy operation that goes all the way down to host.
>
> Signed-off-by: Asias He <asias@xxxxxxxxxx>
> ---
Here are some performance numbers on qemu:
Before:
-------------------------------------
seq-read : io=0 B, bw=269730KB/s, iops=67432 , runt= 62200msec
seq-write : io=0 B, bw=339716KB/s, iops=84929 , runt= 49386msec
rand-read : io=0 B, bw=270435KB/s, iops=67608 , runt= 62038msec
rand-write: io=0 B, bw=354436KB/s, iops=88608 , runt= 47335msec
clat (usec): min=101 , max=138052 , avg=14822.09, stdev=11771.01
clat (usec): min=96 , max=81543 , avg=11798.94, stdev=7735.60
clat (usec): min=128 , max=140043 , avg=14835.85, stdev=11765.33
clat (usec): min=109 , max=147207 , avg=11337.09, stdev=5990.35
cpu : usr=15.93%, sys=60.37%, ctx=7764972, majf=0, minf=54
cpu : usr=32.73%, sys=120.49%, ctx=7372945, majf=0, minf=1
cpu : usr=18.84%, sys=58.18%, ctx=7775420, majf=0, minf=1
cpu : usr=24.20%, sys=59.85%, ctx=8307886, majf=0, minf=0
vdb: ios=8389107/8368136, merge=0/0, ticks=19457874/14616506,
in_queue=34206098, util=99.68%
43: interrupt in total: 887320
fio --exec_prerun="echo 3 > /proc/sys/vm/drop_caches" --group_reporting
--ioscheduler=noop --thread --bs=4k --size=512MB --direct=1 --numjobs=16
--ioengine=libaio --iodepth=64 --loops=3 --ramp_time=0
--filename=/dev/vdb --name=seq-read --stonewall --rw=read
--name=seq-write --stonewall --rw=write --name=rnd-read --stonewall
--rw=randread --name=rnd-write --stonewall --rw=randwrite
After:
-------------------------------------
seq-read : io=0 B, bw=309503KB/s, iops=77375 , runt= 54207msec
seq-write : io=0 B, bw=448205KB/s, iops=112051 , runt= 37432msec
rand-read : io=0 B, bw=311254KB/s, iops=77813 , runt= 53902msec
rand-write: io=0 B, bw=377152KB/s, iops=94287 , runt= 44484msec
clat (usec): min=81 , max=90588 , avg=12946.06, stdev=9085.94
clat (usec): min=57 , max=72264 , avg=8967.97, stdev=5951.04
clat (usec): min=29 , max=101046 , avg=12889.95, stdev=9067.91
clat (usec): min=52 , max=106152 , avg=10660.56, stdev=4778.19
cpu : usr=15.05%, sys=57.92%, ctx=7710941, majf=0, minf=54
cpu : usr=26.78%, sys=101.40%, ctx=7387891, majf=0, minf=2
cpu : usr=19.03%, sys=58.17%, ctx=7681976, majf=0, minf=8
cpu : usr=24.65%, sys=58.34%, ctx=8442632, majf=0, minf=4
vdb: ios=8389086/8361888, merge=0/0, ticks=17243780/12742010,
in_queue=30078377, util=99.59%
43: interrupt in total: 1259639
fio --exec_prerun="echo 3 > /proc/sys/vm/drop_caches" --group_reporting
--ioscheduler=noop --thread --bs=4k --size=512MB --direct=1 --numjobs=16
--ioengine=libaio --iodepth=64 --loops=3 --ramp_time=0
--filename=/dev/vdb --name=seq-read --stonewall --rw=read
--name=seq-write --stonewall --rw=write --name=rnd-read --stonewall
--rw=randread --name=rnd-write --stonewall --rw=randwrite
> drivers/block/virtio_blk.c | 19 +++++++++++--------
> 1 file changed, 11 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 53b81d5..0bdde8f 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -274,15 +274,18 @@ static void virtblk_done(struct virtqueue *vq)
> unsigned int len;
>
> spin_lock_irqsave(vblk->disk->queue->queue_lock, flags);
> - while ((vbr = virtqueue_get_buf(vblk->vq, &len)) != NULL) {
> - if (vbr->bio) {
> - virtblk_bio_done(vbr);
> - bio_done = true;
> - } else {
> - virtblk_request_done(vbr);
> - req_done = true;
> + do {
> + virtqueue_disable_cb(vq);
> + while ((vbr = virtqueue_get_buf(vblk->vq, &len)) != NULL) {
> + if (vbr->bio) {
> + virtblk_bio_done(vbr);
> + bio_done = true;
> + } else {
> + virtblk_request_done(vbr);
> + req_done = true;
> + }
> }
> - }
> + } while (!virtqueue_enable_cb(vq));
> /* In case queue is stopped waiting for more buffers. */
> if (req_done)
> blk_start_queue(vblk->disk->queue);
>
--
Asias
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