Re: 2.4.10-ac10-preempt lmbench output.

From: Andrea Arcangeli (
Date: Tue Oct 09 2001 - 20:18:03 EST

On Tue, Oct 09, 2001 at 08:36:56PM -0400, safemode wrote:
> mp3 player to skip, though. That probably wont be fixed intil 2.5, since
> you need to have preemption in the vm and the rest of the kernel.

xmms skips during I/O should have nothing to do with preemption.

As Alan noted for the ring of dma fragments to expire you need a
scheduler latency of the order of seconds, now (assuming the ll points
in read/write paths) when we've bad latencies under writes it's of the
order of 10msec and it can be turned down further by putting preemption
checks in the buffer lru lists write paths.

The reason xmms skips I believe is because the vm is doing write
throttling. I've at least one idea on how to fix it but it has nothing
to do with preemption in the VM or whatever else scheduler related

So I wouldn't expect to fix any playback skips where buffering is
possible by using the preemptive patch etc.. It's nearly impossible that
it makes any difference.

The preemptive patch can matter only if you're doing real time signal
processing where any kind of buffering isn't possible.

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This archive was generated by hypermail 2b29 : Mon Oct 15 2001 - 21:00:28 EST