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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,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 9D6EAC04AA7 for ; Mon, 13 May 2019 11:35:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6C6A52070D for ; Mon, 13 May 2019 11:35:28 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="A1fzvHen" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728967AbfEMLf1 (ORCPT ); Mon, 13 May 2019 07:35:27 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:51734 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727903AbfEMLf1 (ORCPT ); Mon, 13 May 2019 07:35:27 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=0jKHovWkj7cxIrQ0X5J93JzH+HcvbEjnDPDSVCLfbu0=; b=A1fzvHenWBFJTS5Js0S8GC2ip 2ijSnUjcwuRiy+YDeghv0WkTfiiQ8yglpfr7Dxp94Oi9X2BFQ/lubsruO1ywjbdF8J2dtAJe51n6D BUHyEEtdJLb3/sGvv1RVC2zbtCtUzAspFX0dFZTzwaoHdUN9iBZ+mkBSSrs2RJCin2iKLLRcijHU8 ox3NqupE6nOmjFsA+ztnAu3XpE5i/jPmfjifXA242Q6oyxllO/RvcZ2Vlb1vNVj3BdjtRj8GyJn1v hNyTOmxQfewaVH0yBWll7rOmiuZYjZm9wNXdo9cqx7Bl+w+m6HWv95Til0hJA99rEUsoZOq8uUPxC B9fC2BYeQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1hQ9En-0003v1-2u; Mon, 13 May 2019 11:35:21 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 410592029F87D; Mon, 13 May 2019 13:35:18 +0200 (CEST) Date: Mon, 13 May 2019 13:35:18 +0200 From: Peter Zijlstra To: Viresh Kumar Cc: songliubraving@fb.com, Ingo Molnar , Vincent Guittot , tkjos@google.com, Daniel Lezcano , quentin.perret@linaro.org, chris.redpath@arm.com, Dietmar.Eggemann@arm.com, linux-kernel@vger.kernel.org, steven.sistare@oracle.com Subject: Re: [RFC V2 2/2] sched/fair: Fallback to sched-idle CPU if idle CPU isn't found Message-ID: <20190513113518.GQ2623@hirez.programming.kicks-ass.net> References: <59b37c56b8fcb834f7d3234e776eaeff74ad117f.1556182965.git.viresh.kumar@linaro.org> <20190510072125.GG2623@hirez.programming.kicks-ass.net> <20190513093418.altqhlhu4zsu75t4@vireshk-i7> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190513093418.altqhlhu4zsu75t4@vireshk-i7> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 13, 2019 at 03:04:18PM +0530, Viresh Kumar wrote: > On 10-05-19, 09:21, Peter Zijlstra wrote: > > I don't hate his per se; but the whole select_idle_sibling() thing is > > something that needs looking at. > > > > There was the task stealing thing from Steve that looked interesting and > > that would render your apporach unfeasible. > > I am surely missing something as I don't see how that patchset will > make this patchset perform badly, than what it already does. Nah; I just misremembered. I know Oracle has a patch set poking at select_idle_siblings() _somewhere_ (as do I), and I just found the wrong one. Basically everybody is complaining select_idle_sibling() is too expensive for checking the entire LLC domain, except for FB (and thus likely some other workloads too) that depend on it to kill their tail latency. But I suppose we could still do this, even if we scan only a subset of the LLC, just keep track of the last !idle CPU running only SCHED_IDLE tasks and pick that if you do not (in your limited scan) find a better candidate.