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

[Justin P. Mattock]

Mike Galbraith wrote:
> 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
>    
Wow, at first I did not notice anything
from your *.sh script, but then a few moments
later, the system became vary sluggish. firefox
takes about 15 seconds to load. OS is mint linux
with the latest HEAD on an imac9,1.

Justin P. Mattock
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