Re: Deadline for video capture

[Nick Piggin]

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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