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

[Takashi Iwai]

At Mon, 12 Jul 2004 17:46:39 -0700,
Andrew Morton wrote:
> 
> Lee Revell <rlrevell@xxxxxxxxxxx> wrote:
> >
> > > resierfs: yes, it's a problem.  I "fixed" it multiple times in 2.4, but the
> >  > fixes ended up breaking the fs in subtle ways and I eventually gave up.
> >  > 
> > 
> >  Interesting.  There is an overwhelming consensus amongst Linux audio
> >  folks that you should use reiserfs for low latency work.
> 
> It seems to be misplaced.  A simple make-a-zillion-teeny-files test here
> exhibits a 14 millisecond holdoff.

Yes, I measured a similar on reiserfs, too.
Creation and deletion of many small files causes high latencies.

The creation latency appears with ext3, too, but vanishes when
preemption is enabled.

The deletion peaks appear on all systems.  It's in the long loop of
shrink_dcache_parent().

IIRC, the RCU tasklet stall was another cause of latency in some very
heavy cases.


But, except for creation/deletion of zillon-files, I've not seen any
big latencies during my tests with reiserfs.  Reading/writing big
files (a few GB) are totally OK on reiserfs, all under 1.5 ms.


Takashi
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