I'm unable to reproduce this issue. The host stays responsive and the
dd command completes in a reasonable amount of time. QEMU does not
exceed the 64-thread pool size.
Please post steps to reproduce the issue using a minimal command-line
without libvirt.
Here is information on my attempt to reproduce the problem:
Guest: Kernel 4.10.8-200.fc25.x86_64
Host: 4.10.11-200.fc25.x86_64
QEMU: qemu.git/master (e619b14746e5d8c0e53061661fd0e1da01fd4d60)
The LV is 1 GB on top of LUKS on a Samsung MZNLN256HCHP SATA SSD drive.
mpstat -P ALL 5 output:
11:02:02 AM CPU %usr %nice %sys %iowait %irq %soft %steal
%guest %gnice %idle
11:02:07 AM all 3.36 0.00 6.22 34.54 0.25 0.50 0.00
3.11 0.00 52.03
11:02:07 AM 0 2.82 0.00 5.63 32.39 0.80 1.21 0.00
3.22 0.00 53.92
11:02:07 AM 1 3.02 0.00 6.04 28.77 0.20 0.20 0.00
3.02 0.00 58.75
11:02:07 AM 2 3.56 0.00 7.71 44.27 0.20 0.40 0.00
2.37 0.00 41.50
11:02:07 AM 3 3.81 0.00 5.61 32.46 0.00 0.40 0.00
4.01 0.00 53.71
vmstat 5 output:
procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
r b swpd free buff cache si so bi bo in cs us sy id wa st
0 0 0 1617404 6484 3541468 0 0 2145 84794 1976 8814 8 8 64 20
0
0 0 0 1619492 6484 3538592 0 0 613 69340 1518 7430 6 7 70 17
0
0 0 0 1618920 6484 3538680 0 0 280 75199 1421 6811 6 7 52 35
0
pidstat -v -p $PID_OF_QEMU 5 output:
11:01:08 AM UID PID threads fd-nr Command
11:02:03 AM 0 13043 67 37 qemu-system-x86
11:02:08 AM 0 13043 67 37 qemu-system-x86
11:02:13 AM 0 13043 67 37 qemu-system-x86
$ sudo x86_64-softmmu/qemu-system-x86_64 -enable-kvm -m 1024 -cpu host \
-device virtio-scsi-pci,id=scsihw0,bus=pci.0,addr=0x5 \
-drive
file=test.img,if=none,id=drive-scsi0,format=raw,cache=none,aio=native,detect-zeroes=on
\
-device
scsi-hd,bus=scsihw0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0,id=scsi0,bootindex=100
\
-drive
file=/dev/path/to/testlv,if=none,id=drive-scsi1,format=raw,cache=none,aio=native,detect-zeroes=on
\
-device
scsi-hd,bus=scsihw0.0,channel=0,scsi-id=0,lun=1,drive=drive-scsi1,id=scsi1,bootindex=101
\
-nographic
guest# dd if=/dev/zero of=/dev/sdb bs=1G count=1 oflag=direct
1+0 records in
1+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 15.0681 s, 71.3 MB/s
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https://bugs.launchpad.net/bugs/1687653
Title:
QEMU-KVM / detect_zeroes causes KVM to start unlimited number of
threads on Guest-Sided High-IO with big Blocksize
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