From patchwork Sun Aug 27 23:31:59 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Qais Yousef X-Patchwork-Id: 13367412 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 04810C83F11 for ; Sun, 27 Aug 2023 23:32:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229506AbjH0XcX (ORCPT ); Sun, 27 Aug 2023 19:32:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59196 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229591AbjH0XcV (ORCPT ); Sun, 27 Aug 2023 19:32:21 -0400 Received: from mail-wm1-x32b.google.com (mail-wm1-x32b.google.com [IPv6:2a00:1450:4864:20::32b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 86292BC for ; Sun, 27 Aug 2023 16:32:18 -0700 (PDT) Received: by mail-wm1-x32b.google.com with SMTP id 5b1f17b1804b1-3fef4b063a7so25449965e9.2 for ; Sun, 27 Aug 2023 16:32:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=layalina-io.20221208.gappssmtp.com; s=20221208; t=1693179137; x=1693783937; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=R5bbOUNHimZNEIeEbsqR6Op3Ym6DwMUs69DrKTMvK38=; b=gDEUL0lSGmBoaPWfsdt3TIy8RSGSnjDc+yuy6jOtCoQs3riTpFg5BcpAg/47t5ETzA uBEBzkWGVCP4rmYz+AG5I7SjwiA9c/DKIO8ce/UbRfn8vZWGo0wWUr4yDFlQvTKut4eg lP3wAziUEizy9Jxu8vPPufPekOxYHt2oTwnTa/b4Qo5f7Jk+D7DjlE3YDfTCSoo5AXdC /bPBxjmM79oD0K37l4OWKzrkMmOb4hud30gdwALN7Mz3swQDfSm/SHint0Ps+6zGXIwu bB3ulNvSk/RkB9hOlHnfkdZO3HOppjPSxbrjVi4S7stzgZwp2uuE35P3TZj46EaAIfNo LAFA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1693179137; x=1693783937; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=R5bbOUNHimZNEIeEbsqR6Op3Ym6DwMUs69DrKTMvK38=; b=OuSSlxk4EwVbz2Gtl9TUZnx8gjV7BFJ/Zfw+8xx+mucnqDQbtyv8v1J+SDVKgGUtbq 3AZhj5T5SPmk0oExDBdH8DW6tcfLccUSAKY0Fscq0JpSdaPj+NVsbdT368jv1+en5/dU XeNd04TMmv7SyQvDz7uk7bDI0ZuVvXEf/ucsNSH3QmZsZqG9Dw7y6Ek94sHFpiQkRFU4 sJaHljVIqzOkRogG37j8KPz9boYrorp3mPhdEM29h7BCLZn6gi0uSw1pq0kcQbuB5RA8 HijYvr0eDI9J3cvVaj37Cy0YcJjUXz0pUKPuQpd38pL2sfoI9isKsfNRN3j9DigFhOUq XwZQ== X-Gm-Message-State: AOJu0YzNd/OD8zNcYalgOgJPqNHgAzHkvGSbXhtBOTr8vmb/4U4432Lg SXCqRAHOlpkziVZdxGEZnMFOtBzA+h65s3MiSwg= X-Google-Smtp-Source: AGHT+IHYSiwQ3pMeW83Szi6hCgZxKzkWheiaQklAzkUroyHg+F/5J5GvycGMIWaS2P3qj3to1YJnLQ== X-Received: by 2002:a7b:ce11:0:b0:401:c636:8f4c with SMTP id m17-20020a7bce11000000b00401c6368f4cmr2111090wmc.3.1693179136997; Sun, 27 Aug 2023 16:32:16 -0700 (PDT) Received: from airbuntu.. (host109-151-228-137.range109-151.btcentralplus.com. [109.151.228.137]) by smtp.gmail.com with ESMTPSA id 21-20020a05600c029500b003fe1a96845bsm12220395wmk.2.2023.08.27.16.32.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 27 Aug 2023 16:32:16 -0700 (PDT) From: Qais Yousef To: Ingo Molnar , Peter Zijlstra , "Rafael J. Wysocki" , Viresh Kumar , Vincent Guittot , Dietmar Eggemann Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Lukasz Luba , Qais Yousef Subject: [RFC PATCH 3/7] sched/fair: Remove magic margin in fits_capacity() Date: Mon, 28 Aug 2023 00:31:59 +0100 Message-Id: <20230827233203.1315953-4-qyousef@layalina.io> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230827233203.1315953-1-qyousef@layalina.io> References: <20230827233203.1315953-1-qyousef@layalina.io> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org 80% margin is a magic value that has served its purpose for now, but it no longer fits the variety of systems exist today. If a system is over powered specifically, this 80% will mean we leave a lot of capacity unused before we decide to upmigrate on HMP system. The upmigration behavior should rely on the fact that a bad decision made will need load balance to kick in to perform misfit migration. And I think this is an adequate definition for what to consider as enough headroom to consider whether a util fits capacity or not. Use the new approximate_util_avg() function to predict the util if the task continues to run for TICK_US. If the value is not strictly less than the capacity, then it must not be placed there, ie considered misfit. Signed-off-by: Qais Yousef (Google) --- kernel/sched/fair.c | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 0b7445cd5af9..facbf3eb7141 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -109,16 +109,31 @@ int __weak arch_asym_cpu_priority(int cpu) } /* - * The margin used when comparing utilization with CPU capacity. + * The util will fit the capacity if it has enough headroom to grow within the + * next tick - which is when any load balancing activity happens to do the + * correction. * - * (default: ~20%) + * If util stays within the capacity before tick has elapsed, then it should be + * fine. If not, then a correction action must happen shortly after it starts + * running, hence we treat it as !fit. + * + * TODO: TICK is not actually accurate enough. balance_interval is the correct + * one to use as the next load balance doesn't not happen religiously at tick. + * Accessing balance_interval might be tricky and will require some refactoring + * first. */ -#define fits_capacity(cap, max) ((cap) * 1280 < (max) * 1024) +static inline bool fits_capacity(unsigned long util, unsigned long capacity) +{ + return approximate_util_avg(util, TICK_USEC) < capacity; +} /* * The margin used when comparing CPU capacities. * is 'cap1' noticeably greater than 'cap2' * + * TODO: use approximate_util_avg() to give something more quantifiable based + * on time? Like 1ms? + * * (default: ~5%) */ #define capacity_greater(cap1, cap2) ((cap1) * 1024 > (cap2) * 1078)