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

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Date:	Fri, 15 Apr 2011 17:14:46 +0800
From:	Wei Gu <wei.gu@...csson.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Eric Dumazet <eric.dumazet@...il.com>
CC:	Alexander Duyck <alexander.h.duyck@...el.com>,
	netdev <netdev@...r.kernel.org>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	Mike Galbraith <efault@....de>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: RE: Low performance Intel 10GE NIC (3.2.10) on 2.6.38 Kernel

Hi,

Is there something that I can provide in order to identify the problem?

-----Original Message-----
From: Peter Zijlstra [mailto:a.p.zijlstra@...llo.nl]
Sent: Friday, April 15, 2011 4:58 PM
To: Eric Dumazet
Cc: Alexander Duyck; Wei Gu; netdev; Kirsher, Jeffrey T; Mike Galbraith; Thomas Gleixner
Subject: Re: Low performance Intel 10GE NIC (3.2.10) on 2.6.38 Kernel

On Thu, 2011-04-14 at 18:57 +0200, Eric Dumazet wrote:
> Le jeudi 14 avril 2011 à 18:56 +0200, Peter Zijlstra a écrit :
> > 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.
> >
> >
> >
>
> Normally, Wei Gu already asked to not use C states.
>
> http://h20000.www2.hp.com/bc/docs/support/SupportManual/c01804533/c018
> 04533.pdf
>
> How can we/he check this ?

Not quite sure, I think powertop has something that measures C-state usage, but if the BIOS is lying to us (pretty good bet since he's using HP crap^W) there's nothing much we can do about that.

Another thing that could be causing pain in NO_HZ transitions is if we're having to switch to timer broadcast mode when we go into NO_HZ, I'm not sure if HP systems are affected by this, nor am I exactly sure which DL580 he's got.


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