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Re: [Qemu-devel] [Bug 1581334] [NEW] qemu + librbd takes high %sy cpu un
From: |
Serge Hallyn |
Subject: |
Re: [Qemu-devel] [Bug 1581334] [NEW] qemu + librbd takes high %sy cpu under high random io workload |
Date: |
Fri, 13 May 2016 15:01:52 -0000 |
affects linux
** Also affects: linux
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1581334
Title:
qemu + librbd takes high %sy cpu under high random io workload
Status in Linux:
New
Status in QEMU:
New
Bug description:
I got an IO problem. When running Qemu + ceph(use librbd), and do a random IO
benchmark or some high load random IO test, it will exhaust all my host cpu on
%sy cpu.
It doesn’t happen all the time, but when it appear it will reproduce every
time I start a random IO benchmark(test with Fio).
And the only way to fix the problem is shutdown my vm and start it, but the
problem will happen again with high random IO load.
Some information:
Vendor : HP
Product : HP ProLiant BL460c Gen9
Kernel : 3.16.0-4-amd64
Disto : Debian
Version : 8.4
Arch : amd64
Qemu : 2.1 ~ 2.6 (Yes, I already test the latest qemu2.6 version,
but still got the problem)
Ceph : Hammer 0.94.5
Librbd : 0.94.5 ~ 10.2 (I rebuild librbd with ceph 10.2 source code,
but the problem still here)
Qemu config : cache=none
Qemu cpu&mem: 4core, 8GB
How can i reproduce the problem?
while :; do bash randwrite.sh ; sleep 3600; done >test.log 2>&1 &
(Sleep 3600 is the key to reproduce my problem. I don’t known how long sleep
suit for reproduce, but one hour sleep is enough. the problem will easy
reproduce after a long sleep, if i keep benchmark running without sleep, i
can't reproduce it)
My randwrite.sh script
----------------------------------------------
#!/bin/sh
sync
echo 3 > /proc/sys/vm/drop_caches
FILENAME=/dev/vdc
RUNTIME=100
BLOCKSIZE=4K
IOENGINE=libaio
RESULTFILE=fio-randwrite.log
IODEPTH=32
RAMP_TIME=5
SIZE=100G
fio --numjobs 10 --norandommap --randrepeat=0 --readwrite=randwrite
--ramp_time=$RAMP_TIME --bs=$BLOCKSIZE --runtime=$RUNTIME --iodepth=$IODEPTH
--filename=$FILENAME --ioengine=$IOENGINE --direct=1 --name=iops_randwrite
--group_reporting | tee $RESULTFILE
----------------------------------------------
What happened after the problem appear?
my vm will got huge IOPS drop. In my case, it will drop from 15000 IOPS to
3500 IOPS. And other thing, my host cpu will exhaust on %sy. Top output like
this.
Qemu Fio benchmark
----------------------------------------------------
Tasks: 284 total, 2 running, 282 sleeping, 0 stopped, 0 zombie
%Cpu0 : 11.8 us, 66.7 sy, 0.0 ni, 21.5 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
%Cpu1 : 12.7 us, 64.9 sy, 0.0 ni, 22.4 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
%Cpu2 : 13.7 us, 64.5 sy, 0.0 ni, 21.7 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
%Cpu3 : 13.2 us, 64.1 sy, 0.0 ni, 22.7 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
%Cpu4 : 11.7 us, 65.4 sy, 0.0 ni, 22.8 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
%Cpu5 : 13.2 us, 64.4 sy, 0.0 ni, 22.4 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
%Cpu6 : 12.4 us, 65.1 sy, 0.0 ni, 22.5 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
%Cpu7 : 13.6 us, 63.8 sy, 0.0 ni, 22.6 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
%Cpu8 : 9.8 us, 73.0 sy, 0.0 ni, 17.2 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
%Cpu9 : 7.8 us, 74.5 sy, 0.0 ni, 17.7 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
%Cpu10 : 6.0 us, 81.4 sy, 0.0 ni, 6.6 id, 0.0 wa, 0.0 hi, 6.0 si, 0.0
st
%Cpu11 : 8.4 us, 79.5 sy, 0.0 ni, 8.8 id, 0.0 wa, 0.0 hi, 3.4 si, 0.0
st
%Cpu12 : 7.6 us, 80.7 sy, 0.0 ni, 7.0 id, 0.0 wa, 0.0 hi, 4.7 si, 0.0
st
%Cpu13 : 7.4 us, 79.9 sy, 0.0 ni, 7.7 id, 0.0 wa, 0.0 hi, 5.0 si, 0.0
st
%Cpu14 : 9.8 us, 75.4 sy, 0.0 ni, 11.4 id, 0.0 wa, 0.0 hi, 3.4 si, 0.0
st
%Cpu15 : 6.7 us, 80.1 sy, 0.0 ni, 10.1 id, 0.0 wa, 0.0 hi, 3.0 si, 0.0
st
%Cpu16 : 9.2 us, 69.2 sy, 0.0 ni, 17.5 id, 0.0 wa, 0.0 hi, 4.1 si, 0.0
st
%Cpu17 : 9.9 us, 66.6 sy, 0.0 ni, 20.1 id, 0.0 wa, 0.0 hi, 3.4 si, 0.0
st
%Cpu18 : 16.6 us, 49.0 sy, 0.0 ni, 34.4 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
%Cpu19 : 16.7 us, 46.4 sy, 0.0 ni, 36.9 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
%Cpu20 : 13.0 us, 50.8 sy, 0.0 ni, 36.1 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
%Cpu21 : 18.9 us, 46.2 sy, 0.0 ni, 34.9 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
%Cpu22 : 12.1 us, 52.9 sy, 0.0 ni, 35.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
%Cpu23 : 15.9 us, 47.6 sy, 0.0 ni, 36.6 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
%Cpu24 : 6.7 us, 62.0 sy, 0.0 ni, 31.3 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
%Cpu25 : 7.6 us, 63.7 sy, 0.0 ni, 28.7 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
%Cpu26 : 8.1 us, 75.8 sy, 0.0 ni, 16.1 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
%Cpu27 : 6.7 us, 73.6 sy, 0.0 ni, 19.7 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
%Cpu28 : 9.2 us, 74.3 sy, 0.0 ni, 16.4 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
%Cpu29 : 8.2 us, 73.3 sy, 0.0 ni, 18.5 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
%Cpu30 : 4.4 us, 73.1 sy, 0.0 ni, 22.4 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
%Cpu31 : 7.5 us, 69.6 sy, 0.0 ni, 22.9 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0
st
KiB Mem: 13217662+total, 3721572 used, 12845504+free, 283228 buffers
KiB Swap: 4194300 total, 0 used, 4194300 free. 2242976 cached Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
30349 root 20 0 25.381g 499892 20640 R 2495 0.4 119:11.98
qemu-system-x86
Anything I do?
I use perf top, profile to debug the problem. It show me that something like
thread deadlock problem. Any I test QEMU with kernel RBD, it work fine.
Here are the perf top output on host.
---------------------------------------------------------------
PerfTop: 12393 irqs/sec kernel:87.3% exact: 0.0% [4000Hz cycles],
(all, 32 CPUs)
-------------------------------------------------------------------------------
75.25% [kernel] [k] _raw_spin_lock
1.17% [kernel] [k] futex_wait_setup
0.86% libc-2.19.so [.] malloc
0.58% [kernel] [k] futex_wake
0.55% libc-2.19.so [.] 0x00000000000ea96f
0.41% [kernel] [k] native_write_msr_safe
---------------------------------------------------------------
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- [Qemu-devel] [Bug 1581334] [NEW] qemu + librbd takes high %sy cpu under high random io workload, chenwqin, 2016/05/13
- Re: [Qemu-devel] [Bug 1581334] [NEW] qemu + librbd takes high %sy cpu under high random io workload,
Serge Hallyn <=
- [Qemu-devel] [Bug 1581334] Re: qemu + librbd takes high %sy cpu under high random io workload, Josh Durgin, 2016/05/13
- Re: [Qemu-devel] [Bug 1581334] [NEW] qemu + librbd takes high %sy cpu under high random io workload, Serge Hallyn, 2016/05/13
- [Qemu-devel] [Bug 1581334] Re: qemu + librbd takes high %sy cpu under high random io workload, chenwqin, 2016/05/13
- [Qemu-devel] [Bug 1581334] Re: qemu + librbd takes high %sy cpu under high random io workload, Jason Dillaman, 2016/05/13
- [Qemu-devel] [Bug 1581334] Re: qemu + librbd takes high %sy cpu under high random io workload, chenwqin, 2016/05/13
- [Qemu-devel] [Bug 1581334] Re: qemu + librbd takes high %sy cpu under high random io workload, chenwqin, 2016/05/14
- [Qemu-devel] [Bug 1581334] Re: qemu + librbd takes high %sy cpu under high random io workload, Jason Dillaman, 2016/05/14