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[Qemu-devel] Re: Guest latency issues due to bdrv_check_byte_request
From: |
Jan Kiszka |
Subject: |
[Qemu-devel] Re: Guest latency issues due to bdrv_check_byte_request |
Date: |
Sun, 18 Apr 2010 20:05:21 +0200 |
User-agent: |
Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666 |
Stefan Hajnoczi wrote:
> Thanks Christoph.
>
> Cached getlength with pread/pwrite:
> % time seconds usecs/call calls errors syscall
> ------ ----------- ----------- --------- --------- ----------------
> 96.97 1.760111 11893 148 4 futex
> 1.61 0.029209 1 46891 2217 select
> 0.28 0.005047 0 64609 timer_gettime
> 0.22 0.004059 0 42745 2578 rt_sigreturn
> 0.22 0.003911 0 46261 timer_settime
> 0.18 0.003280 1093 3 shmdt
> 0.17 0.003095 0 23859 pread <---
> 0.17 0.003061 0 42800 write
> 0.16 0.002916 0 47759 5151 read
> 0.02 0.000285 0 645 writev
> [...]
> 0.00 0.000000 0 13 lseek
>
> Note that this is a Tiny Core Linux boot from disk and shutdown; not
> very I/O intensive since it only loads a kernel and ~10 MB initramfs
> without touching the disk much after kernel load.
Nice. Will give this a try tomorrow with "a bit" more load.
We already played with a hack to completely remove the checks from AIO
requests, thus avoiding lseek this way - effect as desired, but fragile
of course.
Jan
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