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=-3.9 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 45FB5C41604 for ; Tue, 6 Oct 2020 07:59:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EBE3820789 for ; Tue, 6 Oct 2020 07:59:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="B0IOu1RR" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726803AbgJFH76 (ORCPT ); Tue, 6 Oct 2020 03:59:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60340 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725912AbgJFH75 (ORCPT ); Tue, 6 Oct 2020 03:59:57 -0400 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7AFDEC061755 for ; Tue, 6 Oct 2020 00:59:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.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=weyj1+oVB2sF+RH5dsw1s1tXmXnPwOyJE9YEld1yZag=; b=B0IOu1RR/yddt4XwCdocTUQ1Cz 5QDOemccGMGKREg1N8rG4xjwZRYdrIcX/9Ztdf/5PC2lgnvFTfTP1Z3434Fshf4VNW5flqP55Sr8N 1iW+cWLDcnpkjQmcp+gYxOvdFUI24JR0eqlcP5ObHj9xytBjo98TPcj4azlsW5og82P9lV602IjU7 bR0EZAtv3GfCnKr4Kmv6arnY8f40Qrek2ZlbETOHr9gsEcUt7f0F2+sHL2tuiKyX9vfVVaXSG+0dI fdCISJ4i7rBwW5UlbNgFXAAaGzqdn4pIK0/QmzIxTdnU6AOmmNtARlcaAVha7zesxa4KzBx+HcVrl n+rgOLDA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kPhss-0004HY-5g; Tue, 06 Oct 2020 07:59:42 +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 29E1F3006D0; Tue, 6 Oct 2020 09:59:40 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id E0C052026833C; Tue, 6 Oct 2020 09:59:39 +0200 (CEST) Date: Tue, 6 Oct 2020 09:59:39 +0200 From: Peter Zijlstra To: tglx@linutronix.de, mingo@kernel.org Cc: linux-kernel@vger.kernel.org, bigeasy@linutronix.de, qais.yousef@arm.com, swood@redhat.com, valentin.schneider@arm.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vincent.donnefort@arm.com, tj@kernel.org Subject: Re: [PATCH -v2 15/17] sched: Fix migrate_disable() vs rt/dl balancing Message-ID: <20201006075939.GL2628@hirez.programming.kicks-ass.net> References: <20201005145717.346020688@infradead.org> <20201005150922.458081448@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201005150922.458081448@infradead.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 05, 2020 at 04:57:32PM +0200, Peter Zijlstra wrote: > +static inline struct task_struct *get_push_task(struct rq *rq) > +{ > + struct task_struct *p = rq->curr; > + > + lockdep_assert_held(&rq->lock); > + > + if (rq->push_busy) > + return NULL; > + > + if (p->nr_cpus_allowed == 1) > + return NULL; This; that means what when we're stuck below a per-cpu thread, we're toast. There's just nothing much you can do... :/ > + > + rq->push_busy = true; > + return get_task_struct(p); > +}