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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_MUTT autolearn=ham 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 5D0D5C43219 for ; Mon, 29 Apr 2019 03:36:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2DF7E2087B for ; Mon, 29 Apr 2019 03:36:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727210AbfD2Dgd (ORCPT ); Sun, 28 Apr 2019 23:36:33 -0400 Received: from out30-132.freemail.mail.aliyun.com ([115.124.30.132]:36970 "EHLO out30-132.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726819AbfD2Dgd (ORCPT ); Sun, 28 Apr 2019 23:36:33 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R971e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e07486;MF=aaron.lu@linux.alibaba.com;NM=1;PH=DS;RN=21;SR=0;TI=SMTPD_---0TQTCbEl_1556508982; Received: from aaronlu(mailfrom:aaron.lu@linux.alibaba.com fp:SMTPD_---0TQTCbEl_1556508982) by smtp.aliyun-inc.com(127.0.0.1); Mon, 29 Apr 2019 11:36:28 +0800 Date: Mon, 29 Apr 2019 11:36:22 +0800 From: Aaron Lu To: Vineeth Remanan Pillai Cc: Nishanth Aravamudan , Julien Desfossez , Peter Zijlstra , Tim Chen , mingo@kernel.org, tglx@linutronix.de, pjt@google.com, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, subhra.mazumdar@oracle.com, fweisbec@gmail.com, keescook@chromium.org, kerrnel@google.com, Phil Auld , Aaron Lu , Aubrey Li , Valentin Schneider , Mel Gorman , Pawan Gupta , Paolo Bonzini Subject: Re: [RFC PATCH v2 11/17] sched: Basic tracking of matching tasks Message-ID: <20190429033620.GA128241@aaronlu> References: <2364f2b65bf50826d881c84d7634b6565dfee527.1556025155.git.vpillai@digitalocean.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2364f2b65bf50826d881c84d7634b6565dfee527.1556025155.git.vpillai@digitalocean.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 23, 2019 at 04:18:16PM +0000, Vineeth Remanan Pillai wrote: > +/* > + * l(a,b) > + * le(a,b) := !l(b,a) > + * g(a,b) := l(b,a) > + * ge(a,b) := !l(a,b) > + */ > + > +/* real prio, less is less */ > +static inline bool __prio_less(struct task_struct *a, struct task_struct *b, bool core_cmp) > +{ > + u64 vruntime; > + > + int pa = __task_prio(a), pb = __task_prio(b); > + > + if (-pa < -pb) > + return true; > + > + if (-pb < -pa) > + return false; > + > + if (pa == -1) /* dl_prio() doesn't work because of stop_class above */ > + return !dl_time_before(a->dl.deadline, b->dl.deadline); > + > + vruntime = b->se.vruntime; > + if (core_cmp) { > + vruntime -= task_cfs_rq(b)->min_vruntime; > + vruntime += task_cfs_rq(a)->min_vruntime; > + } > + if (pa == MAX_RT_PRIO + MAX_NICE) /* fair */ > + return !((s64)(a->se.vruntime - vruntime) <= 0); > + > + return false; > +} This unfortunately still doesn't work. Consider the following task layout on two sibling CPUs(cpu0 and cpu1): rq0.cfs_rq rq1.cfs_rq | | se_bash se_hog se_hog is the sched_entity for a cpu intensive task and se_bash is the sched_entity for bash. There are two problems: 1 SCHED_DEBIT when user execute some commands through bash, say ls, bash will fork. The newly forked ls' vruntime is set in the future due to SCHED_DEBIT. This made 'ls' lose in __prio_less() when compared with hog, whose vruntime may very likely be the same as its cfs_rq's min_vruntime. This is OK since we do not want forked process to starve already running ones. The problem is, since hog keeps running, its vruntime will always sync with its cfs_rq's min_vruntime. OTOH, 'ls' can not run, its cfs_rq's min_vruntime doesn't proceed, making 'ls' always lose to hog. 2 who schedules, who wins so I disabled SCHED_DEBIT, for testing's purpose. When cpu0 schedules, ls could win where both sched_entity's vruntime is the same as their cfs_rqs' min_vruntime. So does hog: when cpu1 schedules, hog can preempt ls in the same way. The end result is, interactive task can lose to cpu intensive task and ls can feel "dead". I haven't figured out a way to solve this yet. A core wide cfs_rq's min_vruntime can probably solve this. Your suggestions are appreciated.