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| From: | address@hidden |
| Subject: | low io performance after loadvm. |
| Date: | Sat, 30 Mar 2024 06:57:04 +0000 |
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Hi team, My qemu start cmd: qemu-system-x86_64 \ -name ubuntu-20.04-vm,debug-threads=on \ -machine pc-i440fx-8.2,usb=off,dump-guest-core=off \ -accel kvm \ -cpu Broadwell-IBRS,vme=on,ss=on,vmx=on,f16c=on,rdrand=on,hypervisor=on,arat=on,tsc-adjust=on,md-clear=on,stibp=on,ssbd=on,xsaveopt=on,pdpe1gb=on,abm=on,tsx-ctrl=off,hle=off,rtm=off \ -m 8192 \ -overcommit mem-lock=off \ -smp 2,sockets=1,dies=1,cores=1,threads=2 \ -numa node,nodeid=0,cpus=0-1,memdev=ram \ -object memory-backend-ram,id=ram,size=8192M \ -uuid d2d68f5d-bff0-4167-bbc3-643e3566b8fb \ -display none \ -nodefaults \ -monitor stdio \ -rtc base=utc,driftfix=slew \ -no-shutdown \ -boot strict=on \ -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 \ -blockdev '{"driver":"file","filename":"/virt/images/focal-server-cloudimg-amd64.img","node-name":"libvirt-4-storage","auto-read-only":true,"discard":"unmap"}' \ -blockdev '{"node-name":"libvirt-4-format","read-only":false,"driver":"qcow2","file":"libvirt-4-storage","backing":null}' \ -device virtio-blk-pci,bus=pci.0,addr=0x4,drive=libvirt-4-format,id=virtio-disk0,bootindex=1 \ -blockdev '{"driver":"file","filename":"/virt/disks/vm1_disk_1.qcow2","node-name":"libvirt-3-storage","auto-read-only":true,"discard":"unmap"}' \ -blockdev '{"node-name":"libvirt-3-format","read-only":false,"driver":"qcow2","file":"libvirt-3-storage","backing":null}' \ -device virtio-blk-pci,bus=pci.0,addr=0x5,drive=libvirt-3-format,id=virtio-disk1 \ -blockdev '{"driver":"file","filename":"/virt/disks/vm1_disk_2.qcow2","node-name":"libvirt-2-storage","auto-read-only":true,"discard":"unmap"}' \ -blockdev '{"node-name":"libvirt-2-format","read-only":false,"driver":"qcow2","file":"libvirt-2-storage","backing":null}' \ -device virtio-blk-pci,bus=pci.0,addr=0x6,drive=libvirt-2-format,id=virtio-disk2 \ -blockdev '{"driver":"file","filename":"/virt/disks/vm1_disk_3.qcow2","node-name":"libvirt-1-storage","auto-read-only":true,"discard":"unmap"}' \ -blockdev '{"node-name":"libvirt-1-format","read-only":false,"driver":"qcow2","file":"libvirt-1-storage","backing":null}' \ -device virtio-blk-pci,bus=pci.0,addr=0x7,drive=libvirt-1-format,id=virtio-disk3 \ -chardev pty,id=charserial0 \ -device isa-serial,chardev=charserial0,id=serial0,index=0 \ -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x2 \ -msg timestamp=on Steps to reproduce: find the following similar msg after launching vm "char device redirected to /dev/pts/1 (label charserial0)" 2. (qemu) info status 3. (qemu) block_set_io_throttle virtio-disk1/virtio-backend 0 0 0 300 0 0 (qemu) block_set_io_throttle virtio-disk2/virtio-backend 0 0 0 300 0 0 (qemu) block_set_io_throttle virtio-disk3/virtio-backend 0 0 0 300 0 0 4. In host, screen /dev/pts/1 (maybe other path) 5. login the VM and run fio on any disk 6. The fio result iops should be 300 test_vdb: (g=0): rw=randwrite, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=sync, iodepth=1 fio-3.16 Starting 1 process Jobs: 1 (f=1): [w(1)][100.0%][w=1201KiB/s][w=300 IOPS][eta 00m:00s] test_vdb: (groupid=0, jobs=1): err= 0: pid=1111: Thu Mar 28 09:08:46 2024 ... 7. (qemu) savevm snapshot1 9. repeat the steps 4, 5, 6 10. The fio result iops should be 300 but it is only 70-80 root@ubuntu:~# fio --name=test_vdb --ioengine=sync --rw=randwrite --bs=4k --size=20G --numjobs=1 --time_based --runtime=30s --filename=/dev/vdb --direct=1 test_vdb: (g=0): rw=randwrite, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=sync, iodepth=1 fio-3.16 Starting 1 process Jobs: 1 (f=1): [w(1)][100.0%][w=344KiB/s][w=86 IOPS][eta 00m:00s] ... my env: Test in 2 qemu versions : ~#qemu-system-x86_64 --version QEMU emulator version 8.2.0 Copyright (c) 2003-2023 Fabrice Bellard and the QEMU Project developers I want to know why the IO has became lower after loadvm? What should I do to avoid this behaviour?
Kevin Xin |
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