Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755336AbXJBRqd (ORCPT ); Tue, 2 Oct 2007 13:46:33 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753130AbXJBRq0 (ORCPT ); Tue, 2 Oct 2007 13:46:26 -0400 Received: from atlrel8.hp.com ([156.153.255.206]:41309 "EHLO atlrel8.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753119AbXJBRqY (ORCPT ); Tue, 2 Oct 2007 13:46:24 -0400 Message-ID: <4702851A.1050100@hp.com> Date: Tue, 02 Oct 2007 13:51:22 -0400 From: "Alan D. Brunelle" User-Agent: Thunderbird 1.5.0.13 (X11/20070824) MIME-Version: 1.0 To: Mathieu Desnoyers Cc: Jens Axboe , linux-kernel@vger.kernel.org, btrace Subject: Re: Linux Kernel Markers - performance characterization with large IO load on large-ish system References: <46F92219.9020406@hp.com> <20070925171349.GA6057@Krystal> <46FA7A86.6090804@hp.com> <20071002122118.GL5236@kernel.dk> <20071002124803.GA23425@Krystal> In-Reply-To: <20071002124803.GA23425@Krystal> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1477 Lines: 45 Mathieu Desnoyers wrote: >> remember that we have seen and discussed something like this before, >> it's still a puzzle to me... >> >> > I do wonder about that performance _increase_ with blktrace enabled. I > > Interesting question indeed. > > In those tests, when blktrace is running, are the relay buffers only > written to or they are also read ? > blktrace (the utility) was running too - so the relay buffere /were/ being read and stored out to disk elsewhere. > Running the tests without consuming the buffers (in overwrite mode) > would tell us more about the nature of the disturbance causing the > performance increase. > I'd have to write a utility to enable the traces, but then not read. Let me think about that. > Also, a kernel trace could help us understand more thoroughly what is > happening there.. is it caused by the scheduler ? memory allocation ? > data cache alignment ? > Yep - when I get some time, I'll look into that. [Clearly not a gating issue for marker support...] > I would suggest that you try aligning the block layer data structures > accessed by blktrace on L2 cacheline size and compare the results (when > blktrace is disabled). > Again, when I get some time! :-) Alan - 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/