From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E7B80C2D0E4 for ; Fri, 20 Nov 2020 18:20:09 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 321D62245B for ; Fri, 20 Nov 2020 18:20:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 321D62245B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 528316B0036; Fri, 20 Nov 2020 13:20:08 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 4D8476B005C; Fri, 20 Nov 2020 13:20:08 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4163F6B005D; Fri, 20 Nov 2020 13:20:08 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0042.hostedemail.com [216.40.44.42]) by kanga.kvack.org (Postfix) with ESMTP id 14B2A6B0036 for ; Fri, 20 Nov 2020 13:20:08 -0500 (EST) Received: from smtpin08.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id B13F02478 for ; Fri, 20 Nov 2020 18:20:07 +0000 (UTC) X-FDA: 77505610854.08.dime07_4414f2d2734d Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin08.hostedemail.com (Postfix) with ESMTP id 8EECD1819E793 for ; Fri, 20 Nov 2020 18:20:07 +0000 (UTC) X-HE-Tag: dime07_4414f2d2734d X-Filterd-Recvd-Size: 2155 Received: from gentwo.org (gentwo.org [3.19.106.255]) by imf13.hostedemail.com (Postfix) with ESMTP for ; Fri, 20 Nov 2020 18:20:07 +0000 (UTC) Received: by gentwo.org (Postfix, from userid 1002) id AB0C33F529; Fri, 20 Nov 2020 18:20:06 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by gentwo.org (Postfix) with ESMTP id A873F3E9FD; Fri, 20 Nov 2020 18:20:06 +0000 (UTC) Date: Fri, 20 Nov 2020 18:20:06 +0000 (UTC) From: Christopher Lameter X-X-Sender: cl@www.lameter.com To: Marcelo Tosatti cc: Matthew Wilcox , linux-mm@kvack.org, Andrew Morton Subject: Re: [PATCH] mm: introduce sysctl file to flush per-cpu vmstat statistics In-Reply-To: <20201117202317.GA282679@fuller.cnet> Message-ID: References: <20201117162805.GA274911@fuller.cnet> <20201117180356.GT29991@casper.infradead.org> <20201117202317.GA282679@fuller.cnet> User-Agent: Alpine 2.22 (DEB 394 2020-01-19) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, 17 Nov 2020, Marcelo Tosatti wrote: > > So what we would need would be something like a sysctl that puts the > > system into a quiet state by completing all workqueue items. Idle all > > subsystems that need it and put the cpu into NOHZ mode. > > Are you suggesting that instead of a specific file to control vmstat > workqueue only, a more generic sysctl could be used? Yes. Introduce a sysctl to quiet down the system. Clean caches that will trigger kernel threads and whatever else is pending on that processor. > About NOHZ mode: the CPU should enter NOHZ automatically as soon as > there is a single thread running, so unclear why that would be needed. There are typically pending actions that still trigger interruptions. If you would immediately quiet down the system if there is only one thread runnable then you would compromise system performance through frequent counter folding and cache cleaning etc.