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 2B07EC4361B for ; Thu, 17 Dec 2020 13:38:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D27322395A for ; Thu, 17 Dec 2020 13:38:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728118AbgLQNif (ORCPT ); Thu, 17 Dec 2020 08:38:35 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56472 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726488AbgLQNie (ORCPT ); Thu, 17 Dec 2020 08:38:34 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 43E89C061794 for ; Thu, 17 Dec 2020 05:37:54 -0800 (PST) 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=2j5SyKzfkhG4+GIahrgxga1F7ov7IQkTMlGIU7JUGvY=; b=vkTdn2bb30CJwK/BdkiV6Uy2AR RCKfmt6VVw14hlI3aSS75HbTuHigTWD9OEJCfpFJx186/bPmddtVGN5Bt0Wpmnj1UTLSTmhv0HCQL 8OQHH0eM2pYtPVvTLYYo8CkayLhFUHbAjAIjq42XGcPDcNqWFKvtcvzxW6WF7sZ0iYsPGkVwf2Iav DAfkktx4G5Zc7lvR5S4hyoe5kuklqFajQzdU9vY7PsrZUI9tWMP9O/U/7w43HJrEig1Stqg540+4E eJb5JBH/74ea8m8pEXIj0bWtmDoK1AyX5TQ7a4oSaFtp9d3R5qSitFPIZnd7okQDmUd/D24eyYrjQ 9ber0chw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kptT1-0006T8-FQ; Thu, 17 Dec 2020 13:37:15 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 01CBB300DAE; Thu, 17 Dec 2020 14:36:56 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id D6C072020D9ED; Thu, 17 Dec 2020 14:36:56 +0100 (CET) Date: Thu, 17 Dec 2020 14:36:56 +0100 From: Peter Zijlstra To: Huaixin Chang Cc: linux-kernel@vger.kernel.org, bsegall@google.com, dietmar.eggemann@arm.com, juri.lelli@redhat.com, mgorman@suse.de, mingo@redhat.com, pauld@redhead.com, pjt@google.com, rostedt@goodmis.org, vincent.guittot@linaro.org, khlebnikov@yandex-team.ru, xiyou.wangcong@gmail.com, shanpeic@linux.alibaba.com Subject: Re: [PATCH 1/4] sched/fair: Introduce primitives for CFS bandwidth burst Message-ID: <20201217133656.GX3040@hirez.programming.kicks-ass.net> References: <20201217074620.58338-1-changhuaixin@linux.alibaba.com> <20201217074620.58338-2-changhuaixin@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201217074620.58338-2-changhuaixin@linux.alibaba.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 17, 2020 at 03:46:17PM +0800, Huaixin Chang wrote: > In this patch, we introduce the notion of CFS bandwidth burst. Unused > "quota" from pervious "periods" might be accumulated and used in the > following "periods". The maximum amount of accumulated bandwidth is > bounded by "burst". And the maximun amount of CPU a group can consume in > a given period is "buffer" which is equivalent to "quota" + "burst in > case that this group has done enough accumulation. Oh man, Juri, wasn't there a paper about statistical bandwidth accounting somewhere? Where, if you replace every utilization by a statistical variable, the end result is still useful? That is, instead of something like; \Sum u_i <= 1, you get something like: \Sum {avg(u),var(u)}_i <= {1, sqrt(\Sum var_i^2)} and you can still proof bounded tardiness etc.. (assuming a gaussian distribution). The proposed seems close to that, but not quite, and I'm afraid it's not quite strong enough to still provide any guarantees.