Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932073AbVLaBPo (ORCPT ); Fri, 30 Dec 2005 20:15:44 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932072AbVLaBPo (ORCPT ); Fri, 30 Dec 2005 20:15:44 -0500 Received: from mustang.oldcity.dca.net ([216.158.38.3]:53694 "HELO mustang.oldcity.dca.net") by vger.kernel.org with SMTP id S932073AbVLaBPe (ORCPT ); Fri, 30 Dec 2005 20:15:34 -0500 Subject: Re: [patch] latency tracer, 2.6.15-rc7 From: Lee Revell To: Linus Torvalds Cc: Ingo Molnar , Dave Jones , Hugh Dickins , linux-kernel In-Reply-To: References: <1135726300.22744.25.camel@mindpipe> <1135814419.7680.13.camel@mindpipe> <20051229082217.GA23052@elte.hu> <20051229100233.GA12056@redhat.com> <20051229101736.GA2560@elte.hu> <1135887072.6804.9.camel@mindpipe> <1135887966.6804.11.camel@mindpipe> <20051229202848.GC29546@elte.hu> <1135908980.4568.10.camel@mindpipe> <20051230080032.GA26152@elte.hu> <1135990270.31111.46.camel@mindpipe> Content-Type: text/plain Date: Fri, 30 Dec 2005 20:15:31 -0500 Message-Id: <1135991732.31111.57.camel@mindpipe> Mime-Version: 1.0 X-Mailer: Evolution 2.5.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1109 Lines: 30 On Fri, 2005-12-30 at 17:02 -0800, Linus Torvalds wrote: > > On Fri, 30 Dec 2005, Lee Revell wrote: > > > > It seems that the networking code's use of RCU can cause 10ms+ > > latencies: > > Hmm. Is there a big jump at the 10ms mark? Do you have a 100Hz timer > source? > > A latency jump at 10ms would tend to indicate a missed wakeup that > was "picked up" by the next timer tick. No there are no large jumps, it really seems that this was the network code causing an RCU callback to drop ~2K routes at once. Specifically RCU invokes dst_rcu_free 2085 times in a single batch (call_rcu_bh(&rt->u.dst.rcu_head, dst_rcu_free) is only called from rt_free() and rt_drop()). I have found that many of the paths in the network stack that can cause high latencies can be tuned via sysctls (for example net.ipv4.route.gc_thresh); this one may be the same. Lee - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/