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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 43D2AC4332F for ; Wed, 8 Nov 2023 10:50:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344761AbjKHKuq (ORCPT ); Wed, 8 Nov 2023 05:50:46 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42458 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344750AbjKHKub (ORCPT ); Wed, 8 Nov 2023 05:50:31 -0500 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 24C1D4789 for ; Wed, 8 Nov 2023 02:47:11 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; 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=ztB9pBHiFR07Il8Vv5GBfT7IWnf46mh1rpUe76Z1+FE=; b=j6aB/r9AvPhSHnZ2k8Xnwo+0Yy pdqDyjhNVN1LOPglg8yHSd5dWVGtI094Cxa4G6FozEGClloZHH8QezTIOo1b0oHPY7dWwvnoysMIP habOzZdjI+IebmFt1ZBHYd60uuY4En7eoedJZptanwhjLlWAfYfo/qGgNhLIleiSm4AyjzZL8oZ39 0Vl/vQvDRG1S32H3qyvEcXRsK5uZF/3YOeNXVoayP4o5WF6/Tv+najNJhrHXPy6trzwbWaBnKqoZB 2tGC0/19M6GHaQBPzH/8imiZMqKayhx0wq6SNXPM9OnL0B2a6owhtyd4xpN4ABtG2IXSYNcoWm1O3 PscoOjHw==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.96 #2 (Red Hat Linux)) id 1r0g4e-00DPVe-0N; Wed, 08 Nov 2023 10:46:16 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id BBC2330049D; Wed, 8 Nov 2023 11:46:15 +0100 (CET) Date: Wed, 8 Nov 2023 11:46:15 +0100 From: Peter Zijlstra To: Ankur Arora Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, torvalds@linux-foundation.org, paulmck@kernel.org, linux-mm@kvack.org, x86@kernel.org, akpm@linux-foundation.org, luto@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, willy@infradead.org, mgorman@suse.de, jon.grimm@amd.com, bharata@amd.com, raghavendra.kt@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com, jgross@suse.com, andrew.cooper3@citrix.com, mingo@kernel.org, bristot@kernel.org, mathieu.desnoyers@efficios.com, geert@linux-m68k.org, glaubitz@physik.fu-berlin.de, anton.ivanov@cambridgegreys.com, mattst88@gmail.com, krypton@ulrich-teichert.org, rostedt@goodmis.org, David.Laight@aculab.com, richard@nod.at, mjguzik@gmail.com Subject: Re: [RFC PATCH 41/86] sched: handle resched policy in resched_curr() Message-ID: <20231108104615.GO8262@noisy.programming.kicks-ass.net> References: <20231107215742.363031-1-ankur.a.arora@oracle.com> <20231107215742.363031-42-ankur.a.arora@oracle.com> <20231108093645.GL8262@noisy.programming.kicks-ass.net> <87fs1gk0bm.fsf@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87fs1gk0bm.fsf@oracle.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 08, 2023 at 02:26:37AM -0800, Ankur Arora wrote: > > Peter Zijlstra writes: > > > On Tue, Nov 07, 2023 at 01:57:27PM -0800, Ankur Arora wrote: > > > >> --- a/kernel/sched/core.c > >> +++ b/kernel/sched/core.c > >> @@ -1027,13 +1027,13 @@ void wake_up_q(struct wake_q_head *head) > >> } > >> > >> /* > >> - * resched_curr - mark rq's current task 'to be rescheduled now'. > >> + * __resched_curr - mark rq's current task 'to be rescheduled'. > >> * > >> - * On UP this means the setting of the need_resched flag, on SMP it > >> - * might also involve a cross-CPU call to trigger the scheduler on > >> - * the target CPU. > >> + * On UP this means the setting of the need_resched flag, on SMP, for > >> + * eager resched it might also involve a cross-CPU call to trigger > >> + * the scheduler on the target CPU. > >> */ > >> -void resched_curr(struct rq *rq) > >> +void __resched_curr(struct rq *rq, resched_t rs) > >> { > >> struct task_struct *curr = rq->curr; > >> int cpu; > >> @@ -1046,17 +1046,77 @@ void resched_curr(struct rq *rq) > >> cpu = cpu_of(rq); > >> > >> if (cpu == smp_processor_id()) { > >> - set_tsk_need_resched(curr, RESCHED_eager); > >> - set_preempt_need_resched(); > >> + set_tsk_need_resched(curr, rs); > >> + if (rs == RESCHED_eager) > >> + set_preempt_need_resched(); > >> return; > >> } > >> > >> - if (set_nr_and_not_polling(curr, RESCHED_eager)) > >> - smp_send_reschedule(cpu); > >> - else > >> + if (set_nr_and_not_polling(curr, rs)) { > >> + if (rs == RESCHED_eager) > >> + smp_send_reschedule(cpu); > > > > I think you just broke things. > > > > Not all idle threads have POLLING support, in which case you need that > > IPI to wake them up, even if it's LAZY. > > Yes, I was concerned about that too. But doesn't this check against the > idle_sched_class in resched_curr() cover that? I that's what that was. Hmm, maybe. I mean, we have idle-injection too, those don't as FIFO, but as such, they can only get preempted from RT/DL, and those will already force preempt anyway. The way you've split and structured the code makes it very hard to follow. Something like: if (set_nr_and_not_polling(curr, rs) && (rs == RESCHED_force || is_idle_task(curr))) smp_send_reschedule(); is *far* clearer, no?