linux-kernel - Re: NO_HZ migration of TCP ack timers

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Date:	Thu, 18 Feb 2010 17:03:30 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Arun R Bharadwaj <arun@...ux.vnet.ibm.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Anton Blanchard <anton@...ba.org>, tglx@...utronix.de,
	davem@...emloft.net, linux-kernel@...r.kernel.org,
	arjan@...radead.org, venkatesh.pallipadi@...el.com
Subject: Re: NO_HZ migration of TCP ack timers

> > > What should we do? Should we use mod_timer_pinned here? Or is this an issue
> > 
> > Sounds like something that should be controlled by the cpufreq governour's
> > idle predictor? Only migrate if predicted idle time is long enough.
> > It's essentially the same problem as deciding how deeply idle to put
> > a CPU. Heavy measures only pay off if the expected time is long enough.
> > 
> 
> cpuidle infrastructure hs statistics about the idle times for
> all the cpus. Maybe we can look to use this infrastructure to decide
> whether to migrate timers or not?

Yes sorry I reallhy meant cpuidle when I wrote cpufreq. 
That's what I suggested too.

But if the problem is lock contention on the target CPU that would
still not completely solve it, just make it less frequent depending
on the idle pattern.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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