From nobody Wed Jan 7 04:02:32 2026 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 E74C0E7849A for ; Mon, 2 Oct 2023 11:55:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236839AbjJBLz1 (ORCPT ); Mon, 2 Oct 2023 07:55:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35426 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236818AbjJBLzV (ORCPT ); Mon, 2 Oct 2023 07:55:21 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E27BCE0; Mon, 2 Oct 2023 04:55:17 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 3EB2B2185F; Mon, 2 Oct 2023 11:55:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1696247716; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=20h7KCpcQajnFp3w5doiMii1hEINmAwyPkgpAacIcrA=; b=0XBgxH/3uEkxE5rwWYDJbxD2pnpq8xEDVD76JmxuUplNhbQCxus67Gd2HPME5sNaH1wKFm EuFx+gtWVWY6vsZjJ2uKdjtxOUQ3I5C/9cpXAec6WUbE26GozoG/xqjnBTj96kl+mF1fh7 suOk9uESkButXiFCFLy68Z0S8VMzHYI= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1696247716; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=20h7KCpcQajnFp3w5doiMii1hEINmAwyPkgpAacIcrA=; b=eYmRgWqpmG+K3u8AaBXjk2wqUQci8T/zb85Zg0nyUDuFvL92prmlP0KqxKcI20NbPwylw8 VX3VNv6BV8z18pBA== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 2777813434; Mon, 2 Oct 2023 11:55:16 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id u2sxCKSvGmVBFAAAMHmgww (envelope-from ); Mon, 02 Oct 2023 11:55:16 +0000 From: Cyril Hrubis To: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Valentin Schneider , linux-kernel@vger.kernel.org, Jonathan Corbet , linux-doc@vger.kernel.org Cc: ltp@lists.linux.it, Cyril Hrubis Subject: [PATCH v3 3/3] docs: scheduler-rt: Use real-time instead of realtime Date: Mon, 2 Oct 2023 13:55:53 +0200 Message-ID: <20231002115553.3007-4-chrubis@suse.cz> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20231002115553.3007-1-chrubis@suse.cz> References: <20231002115553.3007-1-chrubis@suse.cz> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Signed-off-by: Cyril Hrubis --- Documentation/scheduler/sched-rt-group.rst | 34 +++++++++++----------- 1 file changed, 17 insertions(+), 17 deletions(-) diff --git a/Documentation/scheduler/sched-rt-group.rst b/Documentation/sch= eduler/sched-rt-group.rst index a16bee8f74c2..d685609ed3d7 100644 --- a/Documentation/scheduler/sched-rt-group.rst +++ b/Documentation/scheduler/sched-rt-group.rst @@ -39,10 +39,10 @@ Most notable: 1.1 The problem --------------- =20 -Realtime scheduling is all about determinism, a group has to be able to re= ly on +Real-time scheduling is all about determinism, a group has to be able to r= ely on the amount of bandwidth (eg. CPU time) being constant. In order to schedule -multiple groups of realtime tasks, each group must be assigned a fixed por= tion -of the CPU time available. Without a minimum guarantee a realtime group c= an +multiple groups of real-time tasks, each group must be assigned a fixed po= rtion +of the CPU time available. Without a minimum guarantee a real-time group = can obviously fall short. A fuzzy upper limit is of no use since it cannot be relied upon. Which leaves us with just the single fixed portion. =20 @@ -50,14 +50,14 @@ relied upon. Which leaves us with just the single fixed= portion. ---------------- =20 CPU time is divided by means of specifying how much time can be spent runn= ing -in a given period. We allocate this "run time" for each realtime group whi= ch -the other realtime groups will not be permitted to use. +in a given period. We allocate this "run time" for each real-time group wh= ich +the other real-time groups will not be permitted to use. =20 -Any time not allocated to a realtime group will be used to run normal prio= rity +Any time not allocated to a real-time group will be used to run normal pri= ority tasks (SCHED_OTHER). Any allocated run time not used will also be picked u= p by SCHED_OTHER. =20 -Let's consider an example: a frame fixed realtime renderer must deliver 25 +Let's consider an example: a frame fixed real-time renderer must deliver 25 frames a second, which yields a period of 0.04s per frame. Now say it will= also have to play some music and respond to input, leaving it with around 80% C= PU time dedicated for the graphics. We can then give this group a run time of= 0.8 @@ -70,7 +70,7 @@ needs only about 3% CPU time to do so, it can do with a 0= .03 * 0.005s =3D of 0.00015s. =20 The remaining CPU time will be used for user input and other tasks. Because -realtime tasks have explicitly allocated the CPU time they need to perform +real-time tasks have explicitly allocated the CPU time they need to perform their tasks, buffer underruns in the graphics or audio can be eliminated. =20 NOTE: the above example is not fully implemented yet. We still @@ -90,12 +90,12 @@ The system wide settings are configured under the /proc= virtual file system: The scheduling period that is equivalent to 100% CPU bandwidth. =20 /proc/sys/kernel/sched_rt_runtime_us: - A global limit on how much time realtime scheduling may use. This is alw= ays + A global limit on how much time real-time scheduling may use. This is al= ways less or equal to the period_us, as it denotes the time allocated from the - period_us for the realtime tasks. Even without CONFIG_RT_GROUP_SCHED ena= bled, - this will limit time reserved to realtime processes. With + period_us for the real-time tasks. Even without CONFIG_RT_GROUP_SCHED en= abled, + this will limit time reserved to real-time processes. With CONFIG_RT_GROUP_SCHED=3Dy it signifies the total bandwidth available to = all - realtime groups. + real-time groups. =20 * Time is specified in us because the interface is s32. This gives an operating range from 1us to about 35 minutes. @@ -110,7 +110,7 @@ The system wide settings are configured under the /proc= virtual file system: The default values for sched_rt_period_us (1000000 or 1s) and sched_rt_runtime_us (950000 or 0.95s). This gives 0.05s to be used by SCHED_OTHER (non-RT tasks). These defaults were chosen so that a run-away -realtime tasks will not lock up the machine but leave a little time to rec= over +real-time tasks will not lock up the machine but leave a little time to re= cover it. By setting runtime to -1 you'd get the old behaviour back. =20 By default all bandwidth is assigned to the root group and new groups get = the @@ -118,10 +118,10 @@ period from /proc/sys/kernel/sched_rt_period_us and a= run time of 0. If you want to assign bandwidth to another group, reduce the root group's bandwid= th and assign some or all of the difference to another group. =20 -Realtime group scheduling means you have to assign a portion of total CPU -bandwidth to the group before it will accept realtime tasks. Therefore you= will -not be able to run realtime tasks as any user other than root until you ha= ve -done that, even if the user has the rights to run processes with realtime +Real-time group scheduling means you have to assign a portion of total CPU +bandwidth to the group before it will accept real-time tasks. Therefore yo= u will +not be able to run real-time tasks as any user other than root until you h= ave +done that, even if the user has the rights to run processes with real-time priority! =20 =20 --=20 2.41.0