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Date: Mon, 14 Jun 2004 14:21:20 -0400 (EDT)
From: Robert Watson <rwatson@FreeBSD.org>
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To: John Baldwin <jhb@FreeBSD.org>
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cc: "David E. O'Brien" <obrien@FreeBSD.org>
Subject: Re: cvs commit: src/sys/amd64/conf GENERIC
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On Mon, 14 Jun 2004, John Baldwin wrote:

> On Sunday 13 June 2004 07:03 pm, David E. O'Brien wrote:
> > obrien      2004-06-13 23:03:57 UTC
> >
> >   FreeBSD src repository
> >
> >   Modified files:
> >     sys/amd64/conf       GENERIC
> >   Log:
> >   The majority of FreeBSD/amd64 machines are SMP, so use ADAPTIVE_MUTEXES
> >   by default to improve performance.
> 
> We don't know if it improves performance yet. :)

Yeah, as I was mentioning to David over the weekend, it's believed to help
performance anecdotally in a number of interesting cases, and if we can
show it helps in a majority of interesting cases (and doesn't
substantially hurt the others) then I think this should actually be in
GENERIC across all platforms, not just amd64.  I also found I
misunderstood his commit message as it seems to suggest it helps SMP at
the cost of UP, but in fact does not say that. 

Kris reported that he experienced some apparent hangs related to running
with ADAPTIVE_MUTEXES and we should resolve if it was actually the cause
or whether it just triggered an existing race. 

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert@fledge.watson.org      Senior Research Scientist, McAfee Research