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=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 9C843C32771 for ; Sun, 19 Jan 2020 00:15:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6E511246A0 for ; Sun, 19 Jan 2020 00:15:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579392930; bh=QxrhY1ZKchdqWCJT4FNp5gz+287Q3KNekwrVRqV+e94=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=eRGu58dOjybIlcSUjkse68DN1jwBS/rxLlw182HjXkTtDsBfMjV22/PLf1rLHWCZX w75qZTpvyiUiBkdWl0uAYVRQhCpMDS8Oa+tB1aTazIxm5WAazJWQbiCIeX/wNWgfk+ JdD5iIidkCAPnHHgtobB1oAF/VlxGyNZKDb+fGVs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727122AbgASAP3 (ORCPT ); Sat, 18 Jan 2020 19:15:29 -0500 Received: from mail.kernel.org ([198.145.29.99]:58616 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727028AbgASAP3 (ORCPT ); Sat, 18 Jan 2020 19:15:29 -0500 Received: from X1 (nat-ab2241.sltdut.senawave.net [162.218.216.4]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9968A2467C; Sun, 19 Jan 2020 00:15:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579392928; bh=QxrhY1ZKchdqWCJT4FNp5gz+287Q3KNekwrVRqV+e94=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=TBXEcN4iqXSY4fSimgm4USfM8u4H+05c1/LKA2xyic31a3LtvlsRc+Vr5e0rvtD/Q Wz+JdoLGxxwOwO4E0xMrZc6/DQXc3Y98Owk9i0ssYJZN9daSwM469C1nMGDXD+t2Sy I4Amt+WEGFpi+Nch/DSPpKghDlp8xhKw99iqRdWo= Date: Sat, 18 Jan 2020 16:15:28 -0800 From: Andrew Morton To: Michal =?ISO-8859-1?Q?Koutn=FD?= Cc: Michal Hocko , Christopher Lameter , LKML , linux-mm@kvack.org Subject: Re: SLUB: purpose of sysfs events on cache creation/removal Message-Id: <20200118161528.94dc18c074aeaa384200486b@linux-foundation.org> In-Reply-To: <20200117171331.GA17179@blackbody.suse.cz> References: <20191127174317.GD26807@dhcp22.suse.cz> <20191204132812.GF25242@dhcp22.suse.cz> <20191204153225.GM25242@dhcp22.suse.cz> <20191204173224.GN25242@dhcp22.suse.cz> <20200106115733.GH12699@dhcp22.suse.cz> <20200109145236.GS4951@dhcp22.suse.cz> <20200109114415.cf01bd3ad30c5c4aec981653@linux-foundation.org> <20200117171331.GA17179@blackbody.suse.cz> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 17 Jan 2020 18:13:31 +0100 Michal Koutn=FD wrote: > Hello. >=20 > On Thu, Jan 09, 2020 at 11:44:15AM -0800, Andrew Morton wrote: > > I looked at it - there wasn't really any compelling followup. > FTR, I noticed udevd consuming non-negligible CPU cycles when doing some > cgroup stress testing. And even extrapolating to less artificial > situations, the udev events seem to cause useless tickling of udevd. >=20 > I used the simple script below > cat measure.sh < sample() { > local n=3D$(echo|awk "END {print int(40/$1)}") >=20 > for i in $(seq $n) ; do > mkdir /sys/fs/cgroup/memory/grp1 ; > echo 0 >/sys/fs/cgroup/memory/grp1/cgroup.procs ; > /usr/bin/sleep $1 ; > echo 0 >/sys/fs/cgroup/memory/cgroup.procs ; > rmdir /sys/fs/cgroup/memory/grp1 ; > done > } >=20 > for d in 0.004 0.008 0.016 0.032 0.064 0.128 0.256 0.5 1 ; do > echo 0 >/sys/fs/cgroup/cpuacct/system.slice/systemd-udevd.service= /cpuacct.usage > time sample $d 2>&1 | grep real > echo -n "udev " > cat /sys/fs/cgroup/cpuacct/system.slice/systemd-udevd.service/cpu= acct.usage > done > EOD >=20 > and I drew the following ballpark conclusion: > 1.7% CPU time at 1 event/s -> 60 event/s 100% cpu >=20 > (The event is one mkdir/migrate/rmdir sequence. Numbers are from dummy > test VM, so take with a grain of salt.) Thanks. What effect does this patch have upon these numbers? >=20 > > If this change should be pursued then can we please have a formal > > resend? > Who's supposed to do that? Typically the author, but not always. If someone else is particularly motivated to get a patch merged up they can take it over.