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=-21.1 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL 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 3BF0BC4727E for ; Wed, 30 Sep 2020 17:35:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DDD6020706 for ; Wed, 30 Sep 2020 17:35:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="ceNwvdw1" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731440AbgI3Rfj (ORCPT ); Wed, 30 Sep 2020 13:35:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33716 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725823AbgI3Rfj (ORCPT ); Wed, 30 Sep 2020 13:35:39 -0400 Received: from mail-yb1-xb4a.google.com (mail-yb1-xb4a.google.com [IPv6:2607:f8b0:4864:20::b4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CAA33C061755 for ; Wed, 30 Sep 2020 10:35:37 -0700 (PDT) Received: by mail-yb1-xb4a.google.com with SMTP id e2so2428389ybc.17 for ; Wed, 30 Sep 2020 10:35:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=sender:date:message-id:mime-version:subject:from:to:cc; bh=wshcNGdTha70JwxbPwuqLCOHL5oIDzKhLikbvh+J0yU=; b=ceNwvdw1B4sjq2Xcoix1tSEApjHzQoAmd/bFG8/8tEpssPEJxYiO6khx1iUpAgqSiF 1InWHY7z74mxFjKPdgyyxVta95BLNjovsD5ccTtDFW/iq2s1XLPXh/MM6N9bXvgkiIh3 Zx0HV8zC+odKlLHRXwPKU2FbDwCcFOSn9OWnhqDaUidTxnrmNBFQyir1ne6862EcOtgk UPMEu+ClJw3/ijN5o3ZqkM/p0d/WxKlfi+5C5Jn6qo1MFN7qov0II2e9Xl/TXQXNy2iV LYa8zpxCLbJE8BoYyOb76qbrqQvaAzm9rMcmQGDkmVaD7bputDhX78DjXnyR5KG8+zdo E5Hw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:message-id:mime-version:subject:from :to:cc; bh=wshcNGdTha70JwxbPwuqLCOHL5oIDzKhLikbvh+J0yU=; b=fzqoebv+cMZrxcW+mYLslu7FKHTjv4d/lwVIcwtlJsB7gdl/2j8dyAT964gXUcQKNv JMIea+Xn9B1JPHoV6NPMVARbcXVmPn3O67jiJgYEyetDng3GWZnXtpO0heH/gt7daVL1 UldAUattcTBscQcT23VNwqRz02zjzXk5vpq8NwS07cAo/b5FsJucBoP6WsaGrq+Ds3vf kiKnrdrruPueeoN8fxnWp8LlVdvMZVJOIob++e4+SZJbWeD8gjYmrnrryaLfub698Qb7 0Uoi1+Px0R482cg54ImEe/DBdfdcFaHBJJrpWUjTYXFsKjpkPU8xse7STMBd3qE3a/aS PBgA== X-Gm-Message-State: AOAM533ariHOJOkb7Zw/PVB41xpNRSDjZWTPIFUCEREeJtCpLJRbX2xM ZvPs3UvtrR6Us9TXg//syj5/Q0B4 X-Google-Smtp-Source: ABdhPJyIJD22w8mY1UwbuU/9ZlK4M0UZNuijd9wi/dhXRJr2VgJee2imBH32Cs3S3q+voSfR7f6Y1YcE Sender: "posk via sendgmr" X-Received: from posk.svl.corp.google.com ([2620:15c:2cd:202:7220:84ff:fe09:7598]) (user=posk job=sendgmr) by 2002:a25:abea:: with SMTP id v97mr4724341ybi.158.1601487336991; Wed, 30 Sep 2020 10:35:36 -0700 (PDT) Date: Wed, 30 Sep 2020 10:35:32 -0700 Message-Id: <20200930173532.1069092-1-posk@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.28.0.709.gb0816b6eb0-goog Subject: [PATCH] sched/fair: tweak pick_next_entity From: Peter Oskolkov To: Ingo Molnar , Peter Zijlstra , Vincent Guittot , Dietmar Eggemann , linux-kernel@vger.kernel.org Cc: Peter Oskolkov , Peter Oskolkov Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Currently, pick_next_entity(...) has the following structure (simplified): [...] if (last_buddy_ok()) result = last_buddy; if (next_buddy_ok()) result = next_buddy; [...] The intended behavior is to prefer next buddy over last buddy; the current code somewhat obfuscates this, and also wastes cycles checking the last buddy when eventually the next buddy is picked up. So this patch refactors two 'ifs' above into [...] if (next_buddy_ok()) result = next_buddy; else if (last_buddy_ok()) result = last_buddy; [...] Signed-off-by: Peter Oskolkov --- kernel/sched/fair.c | 20 ++++++++++---------- 1 file changed, 10 insertions(+), 10 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index fc3410b8b990..cec6cf9b2bb3 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4465,17 +4465,17 @@ pick_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *curr) se = second; } - /* - * Prefer last buddy, try to return the CPU to a preempted task. - */ - if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1) - se = cfs_rq->last; - - /* - * Someone really wants this to run. If it's not unfair, run it. - */ - if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1) + if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1) { + /* + * Someone really wants this to run. If it's not unfair, run it. + */ se = cfs_rq->next; + } else if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1) { + /* + * Prefer last buddy, try to return the CPU to a preempted task. + */ + se = cfs_rq->last; + } clear_buddies(cfs_rq, se); -- 2.28.0.709.gb0816b6eb0-goog