Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754179Ab0BJPXs (ORCPT ); Wed, 10 Feb 2010 10:23:48 -0500 Received: from borg.medozas.de ([188.40.89.202]:35208 "EHLO borg.medozas.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753151Ab0BJPXr (ORCPT ); Wed, 10 Feb 2010 10:23:47 -0500 Date: Wed, 10 Feb 2010 16:23:33 +0100 (CET) From: Jan Engelhardt To: jens.axboe@oracle.com Subject: Re: kswapd continuously active In-Reply-To: <20100208140837.GN1025@kernel.dk> Message-ID: References: <20100208140837.GN1025@kernel.dk> User-Agent: Alpine 2.01 (LSU 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1979 Lines: 45 Hi, >On Mon, Feb 08 2010, Jan Engelhardt wrote: > >> Could it be that there is something synchronize_rcu()-like in the >> game that-- as a result of how RCU works-- just takes ages with 24 >> VCPUs? > >The only synchronize_rcu() involved in the writeback code happens when >a bdi exits, so you should not hit that. It'll do call_rcu() for work >completions, but 1) you should not see a lot of work entries, and 2) >lots of other kernel code will do that, too. > >Are you seeing a lot of CPU usage? What does eg perf top -a say? top - 16:19:42 up 1:02, 3 users, load average: 3.05, 3.87, 3.51 Cpu(s): 0.0%us, 0.2%sy, 0.0%ni, 98.2%id, 1.6%wa, 0.0%hi, 0.0%si, 0.0%st Mem: 8063800k total, 6676472k used, 1387328k free, 767040k buffers Swap: 0k total, 0k used, 0k free, 4775464k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 26354 root 20 0 3472 1704 1184 R 4 0.0 0:00.33 top 26198 jengelh 20 0 2864 1368 1152 S 4 0.0 0:03.72 watch 574 root 20 0 0 0 0 D 3 0.0 0:52.20 jbd2/sda6-8 312 root 20 0 0 0 0 R 1 0.0 0:29.29 flush-8:0 1 root 20 0 2408 936 808 S 0 0.0 0:01.13 init When it comes down hard, i.e. when there is always new data arriving while sys_sync is working, the loadavg is usually in the range of 1.0*CPUs up to 2.0*CPUs. The top dump shown here is after quiescing writers. >And what setup is this, I didn't realize you were running a virtualized >setup? It is real; but I usually use the term VCPU because this iron has 1 CPU with 6 cores with 24 threads, not 24 CPU (packages). -- 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/