From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: loaded router, excessive getnstimeofday in oprofile Date: Wed, 27 Aug 2008 15:18:24 -0700 (PDT) Message-ID: <20080827.151824.14173512.davem@davemloft.net> References: <87vdxmr53f.fsf@basil.nowhere.org> <48B57BD3.5050206@hp.com> <20080827162735.GW26610@one.firstfloor.org> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: rick.jones2@hp.com, johnpol@2ka.mipt.ru, dada1@cosmosbay.com, denys@visp.net.lb, netdev@vger.kernel.org, linux-kernel@vger.kernel.org To: andi@firstfloor.org Return-path: Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:47893 "EHLO sunset.davemloft.net" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1753199AbYH0WS2 (ORCPT ); Wed, 27 Aug 2008 18:18:28 -0400 In-Reply-To: <20080827162735.GW26610@one.firstfloor.org> Sender: netdev-owner@vger.kernel.org List-ID: From: Andi Kleen Date: Wed, 27 Aug 2008 18:27:35 +0200 > > Those banks really want to crank down on latency - to the point they > > start disabling interrupt coalescing. I bet they'd toss anything out > > they could to shave another microsecond. > > This change would actually likely lower their latency. They want the timestamps, but they want it to match when the packet arrived at their system as closely as is reasonably possible. Socket based solutions don't do that, because we can be sleeping on GFP_KERNEL memory or similar with the socket locked, and thus not be able to set the timestamp until the task wakes up and processes the backlog.