netdev - Re: Low performance Intel 10GE NIC (3.2.10) on 2.6.38 Kernel

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Date:	Thu, 14 Apr 2011 18:56:42 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Alexander Duyck <alexander.h.duyck@...el.com>
Cc:	Wei Gu <wei.gu@...csson.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	netdev <netdev@...r.kernel.org>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	Mike Galbraith <efault@....de>
Subject: Re: Low performance Intel 10GE NIC (3.2.10) on 2.6.38 Kernel

On Thu, 2011-04-14 at 09:42 -0700, Alexander Duyck wrote:

> I'm doing some more digging into this now.  One thought that occurred to 
> me is that if the patch you mention is having some sort of effect this 
> could be a sign of perhaps a kernel timer or scheduling problem.

Right, so the removal of the NO_HZ throttle will allow the CPU to go
into C states more often, this could result in longer wake-up times for
IRQs.

We reverted because:
  - it caused significant battery drain due to not going into C states
    often enough, and
  - its a much better idea to implement these things in the idle
    governor since it already has the job of guestimating the idle
    duration.

I really can't remember back far enough to even come up with a theory of
why kernels prior to merging the NO_HZ throttle would not exhibit this
problem.



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