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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=ham 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 B373BC7618F for ; Mon, 22 Jul 2019 17:34:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 99BA421903 for ; Mon, 22 Jul 2019 17:34:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728353AbfGVRec (ORCPT ); Mon, 22 Jul 2019 13:34:32 -0400 Received: from shelob.surriel.com ([96.67.55.147]:37862 "EHLO shelob.surriel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727908AbfGVReX (ORCPT ); Mon, 22 Jul 2019 13:34:23 -0400 Received: from imladris.surriel.com ([96.67.55.152]) by shelob.surriel.com with esmtpsa (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.92) (envelope-from ) id 1hpcC8-0003HL-8b; Mon, 22 Jul 2019 13:33:52 -0400 From: Rik van Riel To: linux-kernel@vger.kernel.org Cc: kernel-team@fb.com, pjt@google.com, dietmar.eggemann@arm.com, peterz@infradead.org, mingo@redhat.com, morten.rasmussen@arm.com, tglx@linutronix.de, mgorman@techsingularity.net, vincent.guittot@linaro.org, Rik van Riel Subject: [PATCH 07/14] sched,cfs: fix zero length timeslice calculation Date: Mon, 22 Jul 2019 13:33:41 -0400 Message-Id: <20190722173348.9241-8-riel@surriel.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190722173348.9241-1-riel@surriel.com> References: <20190722173348.9241-1-riel@surriel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The way the time slice length is currently calculated, not only do high priority tasks get longer time slices than low priority tasks, but due to fixed point math, low priority tasks could end up with a zero length time slice. This can lead to cache thrashing and other inefficiencies. Cap the minimum time slice length to sysctl_sched_min_granularity. Tasks that end up getting a time slice length too long for their relative priority will simply end up having their vruntime advanced much faster than other tasks, resulting in them receiving time slices less frequently. Signed-off-by: Rik van Riel --- kernel/sched/fair.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 39f7a2d810e1..9ff69b927a3c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -732,6 +732,13 @@ static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity *se) } slice = __calc_delta(slice, se->load.weight, load); } + + /* + * To avoid cache thrashing, run at least sysctl_sched_min_granularity. + * The vruntime of a low priority task advances faster; those tasks + * will simply get time slices less frequently. + */ + slice = max_t(u64, slice, sysctl_sched_min_granularity); return slice; } -- 2.20.1