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authorAsias He2012-09-25 10:36:17 +0800
committerRusty Russell2012-09-28 15:05:16 +0930
commitbb8111086c12ebdadc0544ba04dccd3aad212ad2 (patch)
tree022f3c9dede717151ba0af38e284068848079ae8
parentd78b519f6b945aef6202bbb5b56f928572e15165 (diff)
virtio-blk: Disable callback in virtblk_done()
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. 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 Signed-off-by: Asias He <asias@redhat.com> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
-rw-r--r--drivers/block/virtio_blk.c19
1 files changed, 11 insertions, 8 deletions
diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 53b81d59059b..0bdde8fba397 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);