Re: [linux-audio-dev] latency performance of 2.4 and 2.5...

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Subject: Re: [linux-audio-dev] latency performance of 2.4 and 2.5...
From: Andrew Morton (akpm_AT_digeo.com)
Date: Mon Oct 14 2002 - 11:36:16 EEST


Joern Nettingsmeier wrote:
>
> some new interesting results with 2.5.42:
>
> http://spunk.dnsalias.org/latencytest/2.5.42/2x256.html
>
> overall much worse, *but* greatly reduced latency peaks (max. 6 ms) as
> compared to 2.5.41:
>
> http://spunk.dnsalias.org/latencytest/2.5.41/2x256.html
>
> here the peaks easily reach 13 ms.

Rather depends on the filesystem. ext3 does its own write scheduling,
and does stuff inside lock_kernel(). It needs a couple of scheduling
points I guess.

I'd expect ext2 to work OK with preemption, but nobody has really
looked yet. Unless you're using ftruncate() (grr.)

> i'm not really sure what to make of this....
> can someone explain ?
>
> andrew, it seems part of your mm patch was merged - is there an updated
> patch around that will add the missing hunks ?

Well 2.5.41 had the big change to the truncate code, which was
a rather important part of this whole effort. I can't immediately
think of a 2.5.42 change which would do this...

But nobody has really got down and dug out the toolkit on
2.5 scheduling latency. I guess I should do that soon.


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