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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D65DAC6FA82 for ; Tue, 20 Sep 2022 18:18:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230270AbiITSSF (ORCPT ); Tue, 20 Sep 2022 14:18:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51742 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229871AbiITSSB (ORCPT ); Tue, 20 Sep 2022 14:18:01 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 9F37467CBA for ; Tue, 20 Sep 2022 11:17:57 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 491CE143D; Tue, 20 Sep 2022 11:18:03 -0700 (PDT) Received: from [192.168.178.6] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A7BBC3F5A1; Tue, 20 Sep 2022 11:17:53 -0700 (PDT) Message-ID: <07193d97-476a-498f-e738-e7920c2fdeea@arm.com> Date: Tue, 20 Sep 2022 20:17:29 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH v4 6/8] sched/fair: Add sched group latency support Content-Language: en-US To: Vincent Guittot Cc: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, linux-kernel@vger.kernel.org, parth@linux.ibm.com, qais.yousef@arm.com, chris.hyser@oracle.com, valentin.schneider@arm.com, patrick.bellasi@matbug.net, David.Laight@aculab.com, pjt@google.com, pavel@ucw.cz, tj@kernel.org, qperret@google.com, tim.c.chen@linux.intel.com, joshdon@google.com References: <20220916080305.29574-1-vincent.guittot@linaro.org> <20220916080305.29574-7-vincent.guittot@linaro.org> <000c2893-feb4-373d-2234-2ca74be94714@arm.com> From: Dietmar Eggemann In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19/09/2022 17:49, Vincent Guittot wrote: > On Mon, 19 Sept 2022 at 13:55, Dietmar Eggemann > wrote: >> >> s/valentin.schneider@arm.com// >> >> On 16/09/2022 10:03, Vincent Guittot wrote: >>> Task can set its latency priority, which is then used to decide to preempt >>> the current running entity of the cfs, but sched group entities still have >>> the default latency offset. >>> >>> Add a latency field in task group to set the latency offset of the >>> sched_eneities of the group, which will be used against other entities in >> >> s/sched_eneities/sched_entity >> >>> the parent cfs when deciding which entity to schedule first. >> >> So latency for cgroups does not follow any (existing) Resource >> Distribution Model/Scheme (Documentation/admin-guide/cgroup-v2.rst)? >> Latency values are only used to compare sched entities at the same level. > > Just like share/cpu.weight value does for time sharing But for this we define it as following the `Weights` scheme. That's why I was asking, >> [...] >> >>> +static int cpu_latency_write_s64(struct cgroup_subsys_state *css, >>> + struct cftype *cft, s64 latency) >>> +{ >> >> There is no [MIN, MAX] checking? > > This is done is sched_group_set_latency() which checks that > abs(latency) < sysctl_sched_latency I see. Nit-picking: Wouldn't this allow to specify a latency offset value for the non-existent `nice = 20`? Highest nice value 19 maps to `973/1024 * sysctl_sched_latency`. > >> >> min_weight = sched_latency_to_weight[0] = -1024 >> max_weight = sched_latency_to_weight[39] = 973 >> >> [MIN, MAX] = [sysctl_sched_latency * min_weight >> NICE_LATENCY_SHIFT, >> sysctl_sched_latency * max_weight >> NICE_LATENCY_SHIFT] >> >> >> With the `cpu.latency` knob user would have to know for example that the >> value is -24,000,000ns to get the same behaviour as for a task latency >> nice = -20 (latency prio = 0) (w/ sysctl_sched_latency = 24ms)? > > Yes, Tejun raised some concerns about adding an interface like nice in > the task group in v2 so I have removed it. > >> >> For `nice` we have `cpu.weight.nice` next to `cpu.weight` in cgroup v2 ? > > If everybody is ok, I can add back the cpu.latency.nice interface in > the v5 in addition to the cpu.latency cpu.weight/cpu.weight.nice interface: echo X > cpu.weight tg->shares 1 10,240 100 1,048,576 10000 104,857,600 echo X > cpu.weight.nice -20 90,891,264 0 1,048,576 19 15,360 Wouldn't then a similar interface for cpu.latency [1..100..10000] and cpu.latency.nice [-20..0..19] make most sense? Raw latency_offset values at interface level are not portable.