linux-kernel - Re: 2.6.24.7-rt8

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Date:	Wed, 21 May 2008 08:47:31 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mike Galbraith <efault@....de>
cc:	LKML <linux-kernel@...r.kernel.org>,
	RT <linux-rt-users@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: 2.6.24.7-rt8


On Wed, 21 May 2008, Mike Galbraith wrote:
> On Tue, 2008-05-20 at 00:46 -0400, Steven Rostedt wrote:
> > We are pleased to announce the 2.6.24.7-rt8 tree, which can be
> > downloaded from the location:
> >
> >   http://rt.et.redhat.com/download/
>
> I ran mysql+oltp (ro) on 2.6.24.7-rt7 and 2.6.25-rt2 to compare
> throughput to their parent trees, and ended up with strange (and
> verified) looking performance curves for both trees.  The changes in
> 2.6.24.7-rt8 and 2.6.25.4-rt3 cured the primary oddities.

The difference between 24-rt7 and 24-rt8 as well as with 25-rt2 and 25-rt3
is the deserialization of rwlocks. The rt patch as always serialized
readers to allow for priority inheritance with rwlocks. I wrote a patch to
break that and allow for multiple readers and still keep the priority
inheritance.

Your test probably had a bottle neck on a rwlock (same for rwsems)
somewhere that the new code solved.

-- Steve
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