From owner-freebsd-arch@FreeBSD.ORG  Wed Oct 10 01:40:37 2007
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Date: Wed, 10 Oct 2007 09:41:25 +0800
From: David Xu <davidxu@FreeBSD.org>
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To: Jeff Roberson <jroberson@chesapeake.net>
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Cc: arch@FreeBSD.org
Subject: Re: Abolishing sleeps in issignal()
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I think the performance problem here is that while sleep queue lock is
already hash scaled, but interruptable msleep still has to pass through
a single lock, the process lock, this is a serious serialization problem 
on SMP machine, especially when machine has 4 or more cores.
Also in most most runtime, process has few signals and job controls,
process lock and unlock should be avoided by checking a thread self's
flag instead, which uses thread lock.

I had ever worked out a patch to avoid the lock contention:
http://people.freebsd.org/~davidxu/patch/PCATCH_optimize.patch

mysql benchmark shows that on dual PIII machine it can improve
performance about 1 or 2 percentage, I had not tested it on 4 core
machine.

Regards,
David Xu