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virtio-blk: Disable callback in virtblk_done()

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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>
This commit is contained in:
Asias He 2012-09-25 10:36:17 +08:00 committed by Rusty Russell
parent d78b519f6b
commit bb8111086c
1 changed files with 11 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
drivers/block/virtio_blk.c
View File

@ -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);