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imf08.hostedemail.com; dkim=none; spf=pass (imf08.hostedemail.com: domain of hdanton@sina.com designates 202.108.3.23 as permitted sender) smtp.mailfrom=hdanton@sina.com; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1680391450; a=rsa-sha256; cv=none; b=OxP9ZBST+q8Bq+QyVApznrv8ai8cBfGc2VUMtnHgZaVUBI6gvrQ6AIHYgXspOckmcU9oPs GvRFg4cTj9Wut6u0JDjH9aiKbwfksbjoW79SRmWslVnAReCzwdqoBOuavPCVUlJXyPNUuT zuDi1eozWF3oEv3iufiWhKoqmuW1isE= X-SMAIL-HELO: localhost.localdomain Received: from unknown (HELO localhost.localdomain)([114.249.59.75]) by sina.com (172.16.97.23) with ESMTP id 6428BCE800015570; Sat, 2 Apr 2023 07:23:22 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com X-SMAIL-MID: 31212654919307 From: Hillf Danton To: Vincent Guittot Cc: mingo@kernel.org, linux-kernel@vger.kernel.org, Peter Zijlstra , rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, corbet@lwn.net, qyousef@layalina.io, joshdon@google.com, timj@gnu.org, kprateek.nayak@amd.com, yu.c.chen@intel.com, youssefesmat@chromium.org, linux-mm@kvack.org, joel@joelfernandes.org, efault@gmx.de Subject: Re: [PATCH 14/17] sched/eevdf: Better handle mixed slice length Date: Sun, 2 Apr 2023 07:23:55 +0800 Message-Id: <20230401232355.336-1-hdanton@sina.com> In-Reply-To: References: <20230328092622.062917921@infradead.org> <20230328110354.562078801@infradead.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: f546bz996x1grpag73e64igmyf4yj9r7 X-Rspam-User: X-Rspamd-Queue-Id: 1B570160005 X-Rspamd-Server: rspam06 X-HE-Tag: 1680391448-968544 X-HE-Meta: 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 dPovAgx0 6JQslBJGIwPlq3mgOnNwl1k3V3QAxA14x1fi5bGhzJDK6V0OLTwQv8ra7J6iP+gX98n2p2F57EVKmLuTncbTLx9zUNugnHeukerGyOxgO6LQn9xhGmI5N3Faz8BDyzQH2tUWd+8ltVeI1dUdvnFJnOy79K9SvZy9m8/BVqARSMKq0peG2TSiQk1vSMQt0UYgMndfMLkb9SNIoFOnqZB1MyLZY5Q== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 31 Mar 2023 17:26:51 +0200 Vincent Guittot > On Tue, 28 Mar 2023 at 13:06, Peter Zijlstra wrote: > > > > @@ -4832,6 +4834,18 @@ place_entity(struct cfs_rq *cfs_rq, stru > > lag = se->vlag; > > > > /* > > + * For latency sensitive tasks; those that have a shorter than > > + * average slice and do not fully consume the slice, transition > > + * to EEVDF placement strategy #2. > > + */ > > + if (sched_feat(PLACE_FUDGE) && > > + cfs_rq->avg_slice > se->slice * cfs_rq->avg_load) { > > + lag += vslice; > > + if (lag > 0) > > + lag = 0; > > By using different lag policies for tasks, doesn't this create > unfairness between tasks ? > > I wanted to stress this situation with a simple use case but it seems > that even without changing the slice, there is a fairness problem: > > Task A always run > Task B loops on : running 1ms then sleeping 1ms > default nice and latency nice prio bot both > each task should get around 50% of the time. > > The fairness is ok with tip/sched/core > but with eevdf, Task B only gets around 30% Convincing evidence for glitch in wakeup preempt.