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DateThu, 22 Jan 2004 16:17:25 +1100
FromNick Piggin <>
SubjectRe: Deadline for video capture

Con Kolivas wrote:

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>
>Hi all
>
>I suspected that the anticipatory scheduler might not have been the best 
>choice for video capture because of the interruption to writes by reads and 
>the subsequent anticipatory delay associated with it.  I have now confirmed 
>that booting with the default anticipatory i/o elevator I get many dropped 
>frames that I don't get if I boot with elevator=deadline. 
>
>briefly: dual 7200 rpm ATA5 IDE drives in software RAID0
>
>I guess there isn't really a lot to do about this, it's a compromise one way 
>or the other. The anticipatory scheduler seems better all round but in this 
>large streaming write situation it doesn't seem ideal. Any sysctl settings I 
>could use to blunt the anticipation just before I do video capture?
>

echo 0 > /sys/block/*/queue/iosched/antic_expire
Turns it off alltogether.
You could also adjust read and write batch expire settings which are
heavily biased toward reads.


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