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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 33187C48BDF for ; Thu, 10 Jun 2021 18:51:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1AC24608FC for ; Thu, 10 Jun 2021 18:51:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230393AbhFJSxe (ORCPT ); Thu, 10 Jun 2021 14:53:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47888 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230351AbhFJSxb (ORCPT ); Thu, 10 Jun 2021 14:53:31 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DBFC0C061574; Thu, 10 Jun 2021 11:51:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=q5QvTqrG2xVL3YDck5+IL8BU+tiEEtCfhbIy/ABm4q4=; b=CU4PzQCpc4kXcm5s/Gn6dBy1bI V+bvyjbmJQGo1ViZ8M3QSJME2yJXvw18DkMN+PtxeOXj+8+8NryifDEg/1SbgFUDgIIQONtiohFJm VczSDtj8wDlrpDsvkX807Py7w3g9QrQJ6Let0xe8y/sGb9k5vj/gtk/+8jRhPjsVvDg9UrJTeHjJo k6w3VKJzl57npRQq7X3vWd935MbBTgXVSAqvWxZeF0o6G+QDvkIu0EutYlEZTsUeV3fau/0QiRj25 zngxTnlIHcTVkM1c25vJcE00sNpDB8t73WJyUxKztTGqU1f/pmgEjjcDqbzb2PadC/+R4VgNC0kkZ dSSrqCaw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94 #2 (Red Hat Linux)) id 1lrPlV-001xP4-Iq; Thu, 10 Jun 2021 18:50:58 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 094783001E4; Thu, 10 Jun 2021 20:50:52 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 8E09F200F8CB3; Thu, 10 Jun 2021 20:50:52 +0200 (CEST) Date: Thu, 10 Jun 2021 20:50:52 +0200 From: Peter Zijlstra To: Waiman Long Cc: Tejun Heo , Zefan Li , Johannes Weiner , Jonathan Corbet , Shuah Khan , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, Andrew Morton , Roman Gushchin , Phil Auld , Juri Lelli Subject: Re: [PATCH 2/5] cgroup/cpuset: Add new cpus.partition type with no load balancing Message-ID: References: <20210603212416.25934-1-longman@redhat.com> <20210603212416.25934-3-longman@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210603212416.25934-3-longman@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 03, 2021 at 05:24:13PM -0400, Waiman Long wrote: > Cpuset v1 uses the sched_load_balance control file to determine if load > balancing should be enabled. Cpuset v2 gets rid of sched_load_balance > as its use may require disabling load balancing at cgroup root. > > For workloads that require very low latency like DPDK, the latency > jitters caused by periodic load balancing may exceed the desired > latency limit. > > When cpuset v2 is in use, the only way to avoid this latency cost is to > use the "isolcpus=" kernel boot option to isolate a set of CPUs. After > the kernel boot, however, there is no way to add or remove CPUs from > this isolated set. For workloads that are more dynamic in nature, that > means users have to provision enough CPUs for the worst case situation > resulting in excess idle CPUs. > > To address this issue for cpuset v2, a new cpuset.cpus.partition type > "root-nolb" is added which allows the creation of a cpuset partition with > no load balancing. This will allow system administrators to dynamically > adjust the size of the no load balancing partition to the current need > of the workload without rebooting the system. I'm confused, why do you need this? Just create a parition for each cpu. From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH 2/5] cgroup/cpuset: Add new cpus.partition type with no load balancing Date: Thu, 10 Jun 2021 20:50:52 +0200 Message-ID: References: <20210603212416.25934-1-longman@redhat.com> <20210603212416.25934-3-longman@redhat.com> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=q5QvTqrG2xVL3YDck5+IL8BU+tiEEtCfhbIy/ABm4q4=; b=CU4PzQCpc4kXcm5s/Gn6dBy1bI V+bvyjbmJQGo1ViZ8M3QSJME2yJXvw18DkMN+PtxeOXj+8+8NryifDEg/1SbgFUDgIIQONtiohFJm VczSDtj8wDlrpDsvkX807Py7w3g9QrQJ6Let0xe8y/sGb9k5vj/gtk/+8jRhPjsVvDg9UrJTeHjJo k6w3VKJzl57npRQq7X3vWd935MbBTgXVSAqvWxZeF0o6G+QDvkIu0EutYlEZTsUeV3fau/0QiRj25 zngxTnlIHcTVkM1c25vJcE00sNpDB8t73WJyUxKztTGqU1f/pmgEjjcDqbzb2PadC/+R4VgNC0kkZ dSSrqCaw==; Content-Disposition: inline In-Reply-To: <20210603212416.25934-3-longman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Waiman Long Cc: Tejun Heo , Zefan Li , Johannes Weiner , Jonathan Corbet , Shuah Khan , cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-doc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kselftest-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Andrew Morton , Roman Gushchin , Phil Auld , Juri Lelli On Thu, Jun 03, 2021 at 05:24:13PM -0400, Waiman Long wrote: > Cpuset v1 uses the sched_load_balance control file to determine if load > balancing should be enabled. Cpuset v2 gets rid of sched_load_balance > as its use may require disabling load balancing at cgroup root. > > For workloads that require very low latency like DPDK, the latency > jitters caused by periodic load balancing may exceed the desired > latency limit. > > When cpuset v2 is in use, the only way to avoid this latency cost is to > use the "isolcpus=" kernel boot option to isolate a set of CPUs. After > the kernel boot, however, there is no way to add or remove CPUs from > this isolated set. For workloads that are more dynamic in nature, that > means users have to provision enough CPUs for the worst case situation > resulting in excess idle CPUs. > > To address this issue for cpuset v2, a new cpuset.cpus.partition type > "root-nolb" is added which allows the creation of a cpuset partition with > no load balancing. This will allow system administrators to dynamically > adjust the size of the no load balancing partition to the current need > of the workload without rebooting the system. I'm confused, why do you need this? Just create a parition for each cpu.