Re: ext3 IO latency measurements (was: Linux 2.6.29)

Andrew Morton
2009-03-26T14:50:27Z

On Thu, 26 Mar 2009 10:06:30 +0100 Ingo Molnar <mingo@elte.hu> wrote:

> And it's not just sys_fsync(). The script i wrote tests file read
> latencies. I have created 1000 files with the same size (all copies
> of kernel/sched.c ;-), and tested their cache-cold plain-cat
> performance via:
>
> for ((i=0;i<1000;i++)); do
> printf "file #%4d, plain reading it took: " $i
> /usr/bin/time -f "%e seconds." cat $i >/dev/null
> done
>
> I.e. plain, supposedly high-prio reads. The result is very common
> hickups in read latencies:
>
> file # 579 (253560 bytes), reading it took: 0.08 seconds.
> file # 580 (253560 bytes), reading it took: 0.05 seconds.
> file # 581 (253560 bytes), reading it took: 0.01 seconds.
> file # 582 (253560 bytes), reading it took: 0.01 seconds.
> file # 583 (253560 bytes), reading it took: 4.61 seconds.
> file # 584 (253560 bytes), reading it took: 1.29 seconds.
> file # 585 (253560 bytes), reading it took: 3.01 seconds.
> file # 586 (253560 bytes), reading it took: 7.74 seconds.
> file # 587 (253560 bytes), reading it took: 3.22 seconds.
> file # 588 (253560 bytes), reading it took: 0.05 seconds.
> file # 589 (253560 bytes), reading it took: 0.36 seconds.
> file # 590 (253560 bytes), reading it took: 7.39 seconds.
> file # 591 (253560 bytes), reading it took: 7.58 seconds.
> file # 592 (253560 bytes), reading it took: 7.90 seconds.
> file # 593 (253560 bytes), reading it took: 8.78 seconds.
> file # 594 (253560 bytes), reading it took: 8.01 seconds.
> file # 595 (253560 bytes), reading it took: 7.47 seconds.
> file # 596 (253560 bytes), reading it took: 11.52 seconds.
> file # 597 (253560 bytes), reading it took: 10.33 seconds.
> file # 598 (253560 bytes), reading it took: 8.56 seconds.
> file # 599 (253560 bytes), reading it took: 7.58 seconds.

(gets deja-vu feelings)

http://lkml.org/lkml/2003/2/21/10

Maybe you should be running a 2.5.61 kernel.