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=-9.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 46349C10F05 for ; Thu, 4 Apr 2019 09:25:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0B8DE20693 for ; Thu, 4 Apr 2019 09:25:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1554369917; bh=g4uu2wiihl9udC8yRPgooMGRTHAVtKIEtVR0lWXz5Xk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=DhzyKkbwGyXWpe61eKbN6/mawBqih1Xae6Sg2pt+JRfV4H6RHZnek1Hj6mFDXCgk9 Ebi/JTghkvPA11xP840eG1Izl8irvIo9d4mvKQj7Z5trF/s3ss1mg1JkwiDUAX2/SA mBmVXn9f5jNT820UFgSFa8Vv3CXVBAXkCWs47ZEI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387651AbfDDJOC (ORCPT ); Thu, 4 Apr 2019 05:14:02 -0400 Received: from mail.kernel.org ([198.145.29.99]:54410 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732728AbfDDJN6 (ORCPT ); Thu, 4 Apr 2019 05:13:58 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (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 60EAE2054F; Thu, 4 Apr 2019 09:13:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1554369237; bh=g4uu2wiihl9udC8yRPgooMGRTHAVtKIEtVR0lWXz5Xk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=xTE2DLXFDVvobOHnWsDp9IWhXODcAOfH8AmzXn3hw82IVbRT1PXQnXyWTRYzmQn/Q uzYD2oPVboI5nxDAbHmT4A9gvVQ0ikr6Clw8T/AI/Rnr0ngqYfyaCnVRsM87EkbSTz SG5nWmQmEqdV2Ugun/R9ltkHHqM4tqtTMHbeQH+o= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Tejun Heo , Sasha Levin Subject: [PATCH 5.0 125/246] cgroup, rstat: Dont flush subtree root unless necessary Date: Thu, 4 Apr 2019 10:47:05 +0200 Message-Id: <20190404084623.534823626@linuxfoundation.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190404084619.236418459@linuxfoundation.org> References: <20190404084619.236418459@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review X-Patchwork-Hint: ignore MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 5.0-stable review patch. If anyone has any objections, please let me know. ------------------ [ Upstream commit b4ff1b44bcd384d22fcbac6ebaf9cc0d33debe50 ] cgroup_rstat_cpu_pop_updated() is used to traverse the updated cgroups on flush. While it was only visiting updated ones in the subtree, it was visiting @root unconditionally. We can easily check whether @root is updated or not by looking at its ->updated_next just as with the cgroups in the subtree. * Remove the unnecessary cgroup_parent() test. The system root cgroup is never updated and thus its ->updated_next is always NULL. No need to test whether cgroup_parent() exists in addition to ->updated_next. * Terminate traverse if ->updated_next is NULL. This can only happen for subtree @root and there's no reason to visit it if it's not marked updated. This reduces cpu consumption when reading a lot of rstat backed files. In a micro benchmark reading stat from ~1600 cgroups, the sys time was lowered by >40%. Signed-off-by: Tejun Heo Signed-off-by: Sasha Levin --- kernel/cgroup/rstat.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c index d503d1a9007c..bb95a35e8c2d 100644 --- a/kernel/cgroup/rstat.c +++ b/kernel/cgroup/rstat.c @@ -87,7 +87,6 @@ static struct cgroup *cgroup_rstat_cpu_pop_updated(struct cgroup *pos, struct cgroup *root, int cpu) { struct cgroup_rstat_cpu *rstatc; - struct cgroup *parent; if (pos == root) return NULL; @@ -115,8 +114,8 @@ static struct cgroup *cgroup_rstat_cpu_pop_updated(struct cgroup *pos, * However, due to the way we traverse, @pos will be the first * child in most cases. The only exception is @root. */ - parent = cgroup_parent(pos); - if (parent && rstatc->updated_next) { + if (rstatc->updated_next) { + struct cgroup *parent = cgroup_parent(pos); struct cgroup_rstat_cpu *prstatc = cgroup_rstat_cpu(parent, cpu); struct cgroup_rstat_cpu *nrstatc; struct cgroup **nextp; @@ -140,9 +139,12 @@ static struct cgroup *cgroup_rstat_cpu_pop_updated(struct cgroup *pos, * updated stat. */ smp_mb(); + + return pos; } - return pos; + /* only happens for @root */ + return NULL; } /* see cgroup_rstat_flush() */ -- 2.19.1