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 C7698C43219 for ; Fri, 26 Apr 2019 14:02:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9BBC2206BA for ; Fri, 26 Apr 2019 14:02:23 +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="A2Ovcpju" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726300AbfDZOCW (ORCPT ); Fri, 26 Apr 2019 10:02:22 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:35682 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726039AbfDZOCW (ORCPT ); Fri, 26 Apr 2019 10:02:22 -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=ngzfdohvXqSUVZnRL5smiig+x3FdhK7oHwWhG+cjpGA=; b=A2OvcpjuZlnGx8SM9RnopTxWZ 6op1Z0KKtOzcNSIOLl1ULOMy0oTEjWC9hNw/TuGeKteeud+h7tpBX9v0VafcMajkOFr1eXk7hpPhi XF40UcNDY6ke5PwBB4HOS43E8icf4hNgQjz01v9m6I+vcq0vA7CYY5PPA+iHI1FvPzTmDDW4znjtf 4L3ISCoJ7xHPFAusgYsE0o2HO+KC3J/vEbKN0cUAbmEsKhH5cpYrXiGt3inB0gvQkAM3iA8rYwQUq +FmJ1GrzhltCUK+D7//8Zmpd0P58nuAtBEvABfgZ1KMKsPzuZr26yOGvtUJ4+0SGwZkcpPx+8dGh3 oOpjJlKQw==; 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 1hK1QZ-0007V3-1q; Fri, 26 Apr 2019 14:02:11 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 3FCB5286B7D80; Fri, 26 Apr 2019 16:02:09 +0200 (CEST) Date: Fri, 26 Apr 2019 16:02:09 +0200 From: Peter Zijlstra To: Vineeth Remanan Pillai Cc: Nishanth Aravamudan , Julien Desfossez , 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 09/17] sched: Introduce sched_class::pick_task() Message-ID: <20190426140209.GA2623@hirez.programming.kicks-ass.net> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Tue, Apr 23, 2019 at 04:18:14PM +0000, Vineeth Remanan Pillai wrote: > +static struct task_struct * > +pick_task_fair(struct rq *rq) > +{ > + struct cfs_rq *cfs_rq = &rq->cfs; > + struct sched_entity *se; > + > + if (!cfs_rq->nr_running) > + return NULL; > + > + do { > + struct sched_entity *curr = cfs_rq->curr; > + > + se = pick_next_entity(cfs_rq, NULL); > + > + if (!(se || curr)) > + return NULL; I didn't get around to reading the original discussion here, but how can that possibly be? I can see !se, in that case curr is still selected. I can also see !curr, in that case curr is put. But I cannot see !se && !curr, per the above check we know cfs_rq->nr_running != 0, so there must be a cfs task to find. This means either curr or se must exist. > + > + if (curr) { > + if (se && curr->on_rq) > + update_curr(cfs_rq); > + > + if (!se || entity_before(curr, se)) > + se = curr; > + } > + > + cfs_rq = group_cfs_rq(se); > + } while (cfs_rq); > + > + return task_of(se); > +}