Hello.
I have a problem with the performance of the guest Linux after live migration.
When I analyze the file I/O latency of the guest using LMbench3, the latency of
the guest on the destination host is about 2 times bigger than the guest on the
source host. As a result that I investigated it, this problem occurs if three
following conditions are right.
1. Use the kernel version 2.6.38.6-26.fc15.x86_64 or later.
2. Execute system calls for low level file I/O (read, write, open etc.) on the
guest.
3. Enable EPT.
Performance cannot decrease on other tests of LMbench3; numerical operation,
context switching, memory latencies etc.
Is this an existing problem ? What should I do to resolve it ?
---
The situation the problem occurs
CPU models : Intel Xeon E3-1245 (Both hosts have same cpu.)
Host kernel : 3.6.4
Host OS : Fedora 16 64bit ver. (Both hosts have same OS.)
Guest OS : Fedora 16 64bit ver., kernel 3.1.0-7.fc16.x86_64
QEMU version : qemu-kvm 1.2.0
QEMU parameter : qemu-kvm -m 1024 -drive file=guest.qcow2,if=virtio \
-boot order=c,menu=on -k ja
(-incoming tcp:192.168.0.51:4444 set only destination)
QEMU command : migrate -d tcp:192.168.0.51:4444
Analyses : LMbench version 3
[Guest on the source host]
$ ./lat_syscall open
Simple open/close: 1.4281 microseconds
$ ./lat_syscall read
Simple read: 0.1416 microseconds
$ ./lat_syscall write
Simple write: 0.1194 microseconds
$ ./lat_fs -s 0
0k 550 98726 247712
1k 383 69751 193985
4k 381 69348 193383
10k 313 54369 155697
[Guest on the source host]
$ ./lat_syscall open
Simple open/close: 1.6126 microseconds
$ ./lat_syscall read
Simple read: 0.2206 microseconds
$ ./lat_syscall write
Simple write: 0.1980 microseconds
$ ./lat_fs -s 0
0k 427 83252 243222
1k 315 60530 191650
4k 184 34535 190947
10k 65 11922 152608
---
Thanks.
Shota Uehara <Shouta.Uehara()jp.yokogawa.com>
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