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

[Andrew Morton <akpm@digeo.com>]

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.