Subject: Re: RCU latency regression in 2.6.16-rc1
From: Lee Revell <rlrevell@joe-job.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
       Linus Torvalds <torvalds@osdl.org>,
       "Paul E. McKenney" <paulmck@us.ibm.com>
In-Reply-To: <20060124080157.GA25855@elte.hu>
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	 <20060124075640.GA24806@elte.hu> <1138089483.2771.81.camel@mindpipe>
	 <20060124080157.GA25855@elte.hu>
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Date: Tue, 24 Jan 2006 03:03:53 -0500
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On Tue, 2006-01-24 at 09:01 +0100, Ingo Molnar wrote:
> * Lee Revell <rlrevell@joe-job.com> wrote:
> 
> > On Tue, 2006-01-24 at 08:56 +0100, Ingo Molnar wrote:
> > > * Lee Revell <rlrevell@joe-job.com> wrote:
> > > 
> > > > I ported the latency tracer to 2.6.16 and got this 13ms latency within 
> > > > a few hours.  This is a regression from 2.6.15.
> > > > 
> > > > It appears that RCU can invoke ipv4_dst_destroy thousands of times in 
> > > > a single batch.
> > > 
> > > could you try the PREEMPT_RCU patch below?
> > 
> > Sure.  If it works do you see this making it in 2.6.16?  Otherwise we 
> > still would have a regression...
> 
> nope, that likely wont make v2.6.16, which is frozen already.
> 

Well, the last latency regression I found, I was told "I wish you'd
caught this at 2.6.15-rc1, something could have been done".  Now I've
found another one at the -rc1 stage, and there's still nothing that can
be done?

Lee

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