Re: RCU latency regression in 2.6.16-rc1

[Ingo Molnar <mingo@elte.hu>]

* Lee Revell <rlrevell@joe-job.com> wrote:

> 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?

i did not say that - it should clearly be fixed for 2.6.16. But 
nevertheless we should do PREEMPT_RCU in v2.6.17, because RCU related 
latencies are hard to fix in general.

	Ingo
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