From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: Network latency regressions from 2.6.22 to 2.6.29 Date: Thu, 16 Apr 2009 15:47:52 -0700 (PDT) Message-ID: <20090416.154752.185818977.davem@davemloft.net> References: <1239905279.3203.30.camel@achroite> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: bhutchings@solarflare.com, netdev@vger.kernel.org To: cl@linux.com Return-path: Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:46939 "EHLO sunset.davemloft.net" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1754983AbZDPWsA (ORCPT ); Thu, 16 Apr 2009 18:48:00 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: From: Christoph Lameter Date: Thu, 16 Apr 2009 15:02:36 -0400 (EDT) > On Thu, 16 Apr 2009, Ben Hutchings wrote: > >> On Thu, 2009-04-16 at 12:10 -0400, Christoph Lameter wrote: >> > The following are results of lantency measurements using udpping >> > (available from http://gentwo.org/ll). It shows that significant latencies >> > were added since 2.6.27. I surely wish we could get back to times below 90 >> > microseconds. >> [...] >> >> This "90 microseconds" figure is specific to a particular driver and >> hardware. Have you verified that it applies to others? The variation >> you've reported is tiny compared to the improvements that can be made or >> lost by hardware tuning. > > The RX delay can influence this of course and so can the driver. But the > measurements are with the same RX delay and the same driver. Variations > are up to 20% which is not tiny and its only due to different kernel > versions. The driver is changing, and that can also be enough.