Re: Poor desktop responsiveness with background I/O-operations

Mike Galbraith
2009-09-20T19:38:42Z

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On Sun, 2009-09-20 at 10:50 +0200, Ulrich Lukas wrote:
> Arjan van de Ven wrote:
> > can you try the following two things?
> >
> > echo 4096 > /sys/block/sda/queue/nr_requests
> > for i in `pidof kjournald` ; do ionice -c1 -p $i ; done
>
> I tried this just now, but it doesn't change things much. I can do a
> more testing later today.

Try ionice -c3 for your dd.

> > I assume you're using CFQ.
>
> Yes, it's CFQ. (see .config of my previous posting)
>
> Filesystem is EXT4.

Mine is ext3.

I can easily reproduce pain. The attached cheezy test script, when run
back to back with no args (stock IO), regularly produces beauties:

Performance counter stats for 'sh -c konsole -e exit':

257.670601 task-clock-msecs # 0.004 CPUs
1036 context-switches # 0.004 M/sec
30 CPU-migrations # 0.000 M/sec
6317 page-faults # 0.025 M/sec
471734719 cycles # 1830.767 M/sec
393365060 instructions # 0.834 IPC
7849464 cache-references # 30.463 M/sec
1038976 cache-misses # 4.032 M/sec

65.766937233 seconds time elapsed

Yup, a full minute to get a binary loaded and fired up. Seems it and
others get evicted by the VM. Getting whatever back into ram is painful
to listen to (poor disk/me.. seek latency eating MUCH time).

Calling script back to back with args 1 (realtime foreground) 3 (idle
background) does best:

Performance counter stats for 'sh -c konsole -e exit':

169.915036 task-clock-msecs # 0.077 CPUs
439 context-switches # 0.003 M/sec
9 CPU-migrations # 0.000 M/sec
6314 page-faults # 0.037 M/sec
363128252 cycles # 2137.117 M/sec
367410945 instructions # 1.012 IPC
5822302 cache-references # 34.266 M/sec
437189 cache-misses # 2.573 M/sec

2.213079979 seconds time elapsed

Args 2 (best effort foreground) and 3 (idle background);

Performance counter stats for 'sh -c konsole -e exit':

176.689856 task-clock-msecs # 0.015 CPUs
357 context-switches # 0.002 M/sec
15 CPU-migrations # 0.000 M/sec
6314 page-faults # 0.036 M/sec
374861947 cycles # 2121.582 M/sec
368929476 instructions # 0.984 IPC
5806286 cache-references # 32.861 M/sec
496651 cache-misses # 2.811 M/sec

12.036165968 seconds time elapsed

-Mike

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