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Asias He authored
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=77109411, 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>
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