From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: Low performance Intel 10GE NIC (3.2.10) on 2.6.38 Kernel Date: Fri, 15 Apr 2011 10:57:37 +0200 Message-ID: <1302857857.2388.158.camel@twins> References: <1302253651.4409.2.camel@edumazet-laptop> <1302267400.4409.22.camel@edumazet-laptop> <1302275223.4409.36.camel@edumazet-laptop> <1302330998.2656.113.camel@edumazet-laptop> <4DA3151B.4030507@intel.com> <1302536577.4605.1.camel@edumazet-laptop> <1302761251.3549.198.camel@edumazet-laptop> <1302762810.3549.233.camel@edumazet-laptop> <4DA723F1.7000901@intel.com> <1302800202.2035.32.camel@laptop> <1302800221.3248.39.camel@edumazet-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Alexander Duyck , Wei Gu , netdev , "Kirsher, Jeffrey T" , Mike Galbraith , Thomas Gleixner To: Eric Dumazet Return-path: Received: from casper.infradead.org ([85.118.1.10]:59513 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751974Ab1DOI54 convert rfc822-to-8bit (ORCPT ); Fri, 15 Apr 2011 04:57:56 -0400 In-Reply-To: <1302800221.3248.39.camel@edumazet-laptop> Sender: netdev-owner@vger.kernel.org List-ID: On Thu, 2011-04-14 at 18:57 +0200, Eric Dumazet wrote: > Le jeudi 14 avril 2011 =C3=A0 18:56 +0200, Peter Zijlstra a =C3=A9cri= t : > > On Thu, 2011-04-14 at 09:42 -0700, Alexander Duyck wrote: > >=20 > > > I'm doing some more digging into this now. One thought that occu= rred to=20 > > > me is that if the patch you mention is having some sort of effect= this=20 > > > could be a sign of perhaps a kernel timer or scheduling problem. > >=20 > > Right, so the removal of the NO_HZ throttle will allow the CPU to g= o > > into C states more often, this could result in longer wake-up times= for > > IRQs. > >=20 > > We reverted because: > > - it caused significant battery drain due to not going into C sta= tes > > 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. > >=20 > > I really can't remember back far enough to even come up with a theo= ry of > > why kernels prior to merging the NO_HZ throttle would not exhibit t= his > > problem. > >=20 > >=20 > >=20 >=20 > Normally, Wei Gu already asked to not use C states. >=20 > http://h20000.www2.hp.com/bc/docs/support/SupportManual/c01804533/c01= 804533.pdf >=20 > 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.