From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: NAPI, e100, and system performance problem Date: 22 Apr 2005 20:30:04 +0200 Message-ID: <20050422183004.GC10598@muc.de> References: <1113855967.7436.39.camel@localhost.localdomain> <20050419055535.GA12211@sgi.com> <1114173195.7679.30.camel@localhost.localdomain> <20050422172108.GA10598@muc.de> <1114193902.7978.39.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Greg Banks , Arthur Kepner , "Brandeburg, Jesse" , netdev@oss.sgi.com, davem@redhat.com Return-path: Date: Fri, 22 Apr 2005 20:30:04 +0200 To: jamal Content-Disposition: inline In-Reply-To: <1114193902.7978.39.camel@localhost.localdomain> Sender: netdev-bounce@oss.sgi.com Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org On Fri, Apr 22, 2005 at 02:18:22PM -0400, jamal wrote: > On Fri, 2005-22-04 at 19:21 +0200, Andi Kleen wrote: > > On Fri, Apr 22, 2005 at 08:33:15AM -0400, jamal wrote: > [..] > > > They should not run slower - but they may consume more CPU. > > > > They actually run slower. > > > > Why do they run slower? There could be 1000 other variables involved? > What is it that makes you so sure it is NAPI? > I know you are capable of proving it is NAPI - please do so. We tested back then by downgrading to an older non NAPI tg3 driver and it made the problem go away :) The broadcom bcm57xx driver which did not support NAPI at this time was also much faster. > > Now before David complains this was with old 2.6 kernels and I dont have > > time right now to rerun the benchmarks, but at least I dont think > > there was ever any patch addressing these issues. > > > > It would be helpful if you use new kernels of course - that reduces the > number of variables to look at. It was customers who use certified SLES kernels. > There is only one complaint I have ever heard about NAPI and it is about > low rates: It consumes more CPU at very low rates. Very low rates It was not only more CPU usage, but actually slower network performance on systems with plenty of CPU power. Also I doubt the workload Jesse and Greg/Arthur/SGI saw also had issues with CPU power (can you guys confirm?) > You are the first person i have heard that says NAPI would be slower > in terms of throughput or latency at low rates. My experiences is there > is no difference between the two at low input rate. It would be > interesting to see the data. Well, did you ever test a non routing workload? -Andi