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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 3EF26C4167B for ; Mon, 7 Dec 2020 15:43:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0CDDB23750 for ; Mon, 7 Dec 2020 15:43:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726840AbgLGPnM (ORCPT ); Mon, 7 Dec 2020 10:43:12 -0500 Received: from outbound-smtp63.blacknight.com ([46.22.136.252]:56139 "EHLO outbound-smtp63.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726754AbgLGPnM (ORCPT ); Mon, 7 Dec 2020 10:43:12 -0500 Received: from mail.blacknight.com (pemlinmail05.blacknight.ie [81.17.254.26]) by outbound-smtp63.blacknight.com (Postfix) with ESMTPS id 1ECE2FA88F for ; Mon, 7 Dec 2020 15:42:19 +0000 (GMT) Received: (qmail 27896 invoked from network); 7 Dec 2020 15:42:18 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.22.4]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 7 Dec 2020 15:42:18 -0000 Date: Mon, 7 Dec 2020 15:42:16 +0000 From: Mel Gorman To: Vincent Guittot Cc: LKML , Aubrey Li , Barry Song , Ingo Molnar , Peter Ziljstra , Juri Lelli , Valentin Schneider , Linux-ARM Subject: Re: [RFC PATCH 0/4] Reduce worst-case scanning of runqueues in select_idle_sibling Message-ID: <20201207154216.GE3371@techsingularity.net> References: <20201207091516.24683-1-mgorman@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 07, 2020 at 04:04:41PM +0100, Vincent Guittot wrote: > On Mon, 7 Dec 2020 at 10:15, Mel Gorman wrote: > > > > This is a minimal series to reduce the amount of runqueue scanning in > > select_idle_sibling in the worst case. > > > > Patch 1 removes SIS_AVG_CPU because it's unused. > > > > Patch 2 improves the hit rate of p->recent_used_cpu to reduce the amount > > of scanning. It should be relatively uncontroversial > > > > Patch 3-4 scans the runqueues in a single pass for select_idle_core() > > and select_idle_cpu() so runqueues are not scanned twice. It's > > a tradeoff because it benefits deep scans but introduces overhead > > for shallow scans. > > > > Even if patch 3-4 is rejected to allow more time for Aubrey's idle cpu mask > > patch 3 looks fine and doesn't collide with Aubrey's work. But I don't > like patch 4 which manipulates different cpumask including > load_balance_mask out of LB and I prefer to wait for v6 of Aubrey's > patchset which should fix the problem of possibly scanning twice busy > cpus in select_idle_core and select_idle_cpu > Seems fair, we can see where we stand after V6 of Aubrey's work. A lot of the motivation for patch 4 would go away if we managed to avoid calling select_idle_core() unnecessarily. As it stands, we can call it a lot from hackbench even though the chance of getting an idle core are minimal. Assuming I revisit it, I'll update the schedstat debug patches to include the times select_idle_core() starts versus how many times it fails and see can I think of a useful heuristic. I'll wait for more review on patches 1-3 and if I hear nothing, I'll resend just those. Thanks Vincent. -- Mel Gorman SUSE Labs 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=-5.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 1C8F3C4361B for ; Mon, 7 Dec 2020 15:43:52 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id D56B523731 for ; Mon, 7 Dec 2020 15:43:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D56B523731 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=techsingularity.net Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=UbhIMJcH6UjJaFAXAWAMyBrSiE/dBTMpp4udwuGCrcc=; b=Gg+wXlh654tuAYCiYgKAqlHHE d+6wMT/l83A6q0Xvn981IMNPil4HOvs938Zib+vW2aWu2VtEgLNejtssPN9GayuawENilrhkAkEH4 zaylu0sjZEK6hI0qvcD9sHQ6tutIKge6afAsQVGDzwLMZHh2p1l5FOm/gaWRm4w5i16Z9064gKfIC O14guPNWU3c1nb4KYhdWl5ofxDOkHNm00WJHELmIi+Ee9MCsMQyJ2ZwVDa+zqnG2mBNEqBxNLOo5m w9b/GvmgDPMvP+n4f1YuUE2AG0fQo8XQSGlAy4XzG+Gv0EaBokUMd7vyTk02h+xL4zBbbzmT658s+ ezmQabIaA==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kmIek-0001z1-SO; Mon, 07 Dec 2020 15:42:30 +0000 Received: from outbound-smtp08.blacknight.com ([46.22.139.13]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kmIei-0001yO-Dl for linux-arm-kernel@lists.infradead.org; Mon, 07 Dec 2020 15:42:29 +0000 Received: from mail.blacknight.com (pemlinmail05.blacknight.ie [81.17.254.26]) by outbound-smtp08.blacknight.com (Postfix) with ESMTPS id 319EA1C3559 for ; Mon, 7 Dec 2020 15:42:19 +0000 (GMT) Received: (qmail 27896 invoked from network); 7 Dec 2020 15:42:18 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.22.4]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 7 Dec 2020 15:42:18 -0000 Date: Mon, 7 Dec 2020 15:42:16 +0000 From: Mel Gorman To: Vincent Guittot Subject: Re: [RFC PATCH 0/4] Reduce worst-case scanning of runqueues in select_idle_sibling Message-ID: <20201207154216.GE3371@techsingularity.net> References: <20201207091516.24683-1-mgorman@techsingularity.net> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201207_104228_561239_4064ED8E X-CRM114-Status: GOOD ( 18.80 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Barry Song , Juri Lelli , Peter Ziljstra , Aubrey Li , LKML , Ingo Molnar , Valentin Schneider , Linux-ARM Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Dec 07, 2020 at 04:04:41PM +0100, Vincent Guittot wrote: > On Mon, 7 Dec 2020 at 10:15, Mel Gorman wrote: > > > > This is a minimal series to reduce the amount of runqueue scanning in > > select_idle_sibling in the worst case. > > > > Patch 1 removes SIS_AVG_CPU because it's unused. > > > > Patch 2 improves the hit rate of p->recent_used_cpu to reduce the amount > > of scanning. It should be relatively uncontroversial > > > > Patch 3-4 scans the runqueues in a single pass for select_idle_core() > > and select_idle_cpu() so runqueues are not scanned twice. It's > > a tradeoff because it benefits deep scans but introduces overhead > > for shallow scans. > > > > Even if patch 3-4 is rejected to allow more time for Aubrey's idle cpu mask > > patch 3 looks fine and doesn't collide with Aubrey's work. But I don't > like patch 4 which manipulates different cpumask including > load_balance_mask out of LB and I prefer to wait for v6 of Aubrey's > patchset which should fix the problem of possibly scanning twice busy > cpus in select_idle_core and select_idle_cpu > Seems fair, we can see where we stand after V6 of Aubrey's work. A lot of the motivation for patch 4 would go away if we managed to avoid calling select_idle_core() unnecessarily. As it stands, we can call it a lot from hackbench even though the chance of getting an idle core are minimal. Assuming I revisit it, I'll update the schedstat debug patches to include the times select_idle_core() starts versus how many times it fails and see can I think of a useful heuristic. I'll wait for more review on patches 1-3 and if I hear nothing, I'll resend just those. Thanks Vincent. -- Mel Gorman SUSE Labs _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel