Re: [linux-audio-dev] Re: [announce] [patch] Voluntary Kernel Preemption Patch

From: Ingo Molnar
Date: Mon Jul 19 2004 - 05:48:58 EST

* Andrew Morton <akpm@xxxxxxxx> wrote:

> > Should I try ext3?
> ext3 is certainly better than that, but still has a couple of
> potential problem spots. ext2 is probably the best at this time.

with the voluntary-preempt patch applied ext3 is below ~500 usecs for
all things i tried on a 2GHz CPU. Without the patch i can trigger
latencies up to milliseconds (even with CONFIG_PREEMPT) by triggering a
bigger commit stream via some large file write or a cached du / causing
a stream of atime updates. (I very much suspect that all other
journalled filesystems have similar problems and they'll need
measurements and fixing just like ext3 does.)

another bigger problem area is the VM - see my patch for details.
pagetable zapping and page reclaim are both problematic and need fixups
even under CONFIG_PREEMPT. Doing a simple 'make -j' kernel build that
hits swap triggers these easily. (after applying my patch the latencies
go below 1msec even with a 'make -j' overload.)

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