From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx155.postini.com [74.125.245.155]) by kanga.kvack.org (Postfix) with SMTP id 1AED66B00A2 for ; Tue, 3 Jan 2012 17:13:25 -0500 (EST) Received: by ggni2 with SMTP id i2so12862097ggn.14 for ; Tue, 03 Jan 2012 14:13:24 -0800 (PST) Message-ID: <4F037D84.5070502@gmail.com> Date: Tue, 03 Jan 2012 17:13:24 -0500 From: KOSAKI Motohiro MIME-Version: 1.0 Subject: Re: [PATCH v5 8/8] mm: add vmstat counters for tracking PCP drains References: <1325499859-2262-1-git-send-email-gilad@benyossef.com> <1325499859-2262-9-git-send-email-gilad@benyossef.com> <4F033F44.6020403@gmail.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Gilad Ben-Yossef Cc: linux-kernel@vger.kernel.org, Christoph Lameter , Chris Metcalf , Peter Zijlstra , Frederic Weisbecker , linux-mm@kvack.org, Pekka Enberg , Matt Mackall , Sasha Levin , Rik van Riel , Andi Kleen , Mel Gorman , Andrew Morton , Alexander Viro , Avi Kivity (1/3/12 2:00 PM), Gilad Ben-Yossef wrote: > 2012/1/3 KOSAKI Motohiro: >> (1/2/12 5:24 AM), Gilad Ben-Yossef wrote: >>> This patch introduces two new vmstat counters: pcp_global_drain >>> that counts the number of times a per-cpu pages global drain was >>> requested and pcp_global_ipi_saved that counts the number of times >>> the number of CPUs with per-cpu pages in any zone were less then >>> 1/2 of the number of online CPUs. >>> >>> The patch purpose is to show the usefulness of only sending an IPI >>> asking to drain per-cpu pages to CPUs that actually have them >>> instead of a blind global IPI. It is probably not useful by itself. > ... > > } >>> on_each_cpu_mask(cpus_with_pcps, drain_local_pages, NULL, 1); >>> + >>> + count_vm_event(PCP_GLOBAL_DRAIN); >>> + if (cpumask_weight(cpus_with_pcps)< (cpumask_weight(cpu_online_mask) / 2)) >>> + count_vm_event(PCP_GLOBAL_IPI_SAVED); >> >> NAK. >> >> PCP_GLOBAL_IPI_SAVED is only useful at development phase. I can't >> imagine normal admins use it. > > As the description explains, the purpose of the patch is to show why i > claim the previous > patch is useful. I did not meant it to be applied to mainline. My > apologies for not > stating this more clearly. I agree it is not useful for an admin, > although perhaps PCP_GLOBAL_DRAIN > alone might - I am not sure? Until we found a good usecase, we shouldn't append any stat. It is not zero overhead even though nobody uses. That's why I almost always disagree adding statistics from point of developers view. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org