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 2A20EC761AF for ; Thu, 23 Mar 2023 17:42:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229681AbjCWRmm (ORCPT ); Thu, 23 Mar 2023 13:42:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41450 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229518AbjCWRml (ORCPT ); Thu, 23 Mar 2023 13:42:41 -0400 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 EDD0330C2; Thu, 23 Mar 2023 10:42:39 -0700 (PDT) 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=uknWkbKCt7r7d+Uri/V39eu4SUqBOmf1+zXqyPceR/Q=; b=dDxw8FpzxhqVLTwZLp+6PLqsZb sRJ3X8JsTwZ/JiVyuRpgwQqpktLFA6bvn6+Z5BUFJqFkJRGddW2MQ80jsQJfIgRgfreJe2ASji3Ok ubgdvdDoJEumb5zC8iamfg/Bj2JpUUoIIkbWbcU+eS2YQIKqSfzW3woiON0TO/xxXdEJFV3HgvHvO sXiZid3LBW1uxBADyBwicyQ2lIEhNgqEfn2o6vq+arvPTl9YSvFX++J11S113A+M+rXKiwhf9f2WT HAcSaWWs+/beDL4nUBnINhc313sBkIdpEH77HQ1cT1mXenwbLj9N8jiiOSWeGoraLKmJYcbpzRY9+ kwRmLaAw==; 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 1pfOwQ-004vDx-2T; Thu, 23 Mar 2023 17:41:35 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 7E8ED3002FC; Thu, 23 Mar 2023 18:41:29 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 68B95240DB73A; Thu, 23 Mar 2023 18:41:29 +0100 (CET) Date: Thu, 23 Mar 2023 18:41:29 +0100 From: Peter Zijlstra To: Valentin Schneider Cc: linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org, linux-ia64@vger.kernel.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, openrisc@lists.librecores.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, x86@kernel.org, "Paul E. McKenney" , Steven Rostedt , Thomas Gleixner , Sebastian Andrzej Siewior , Juri Lelli , Daniel Bristot de Oliveira , Marcelo Tosatti , Frederic Weisbecker , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Marc Zyngier , Mark Rutland , Russell King , Nicholas Piggin , Guo Ren , "David S. Miller" Subject: Re: [PATCH v5 7/7] sched, smp: Trace smp callback causing an IPI Message-ID: <20230323174129.GA2753619@hirez.programming.kicks-ass.net> References: <20230307143558.294354-1-vschneid@redhat.com> <20230307143558.294354-8-vschneid@redhat.com> <20230322095329.GS2017917@hirez.programming.kicks-ass.net> <20230322140434.GC2357380@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-csky@vger.kernel.org On Thu, Mar 23, 2023 at 04:25:25PM +0000, Valentin Schneider wrote: > On 22/03/23 15:04, Peter Zijlstra wrote: > > @@ -798,14 +794,20 @@ static void smp_call_function_many_cond( > > } > > > > /* > > + * Trace each smp_function_call_*() as an IPI, actual IPIs > > + * will be traced with func==generic_smp_call_function_single_ipi(). > > + */ > > + trace_ipi_send_cpumask(cfd->cpumask_ipi, _RET_IP_, func); > > I just got a trace pointing out this can emit an event even though no IPI > is sent if e.g. the cond_func predicate filters all CPUs in the argument > mask: > > ipi_send_cpumask: cpumask= callsite=on_each_cpu_cond_mask+0x3c callback=flush_tlb_func+0x0 > > Maybe something like so on top? > > --- > diff --git a/kernel/smp.c b/kernel/smp.c > index ba5478814e677..1dc452017d000 100644 > --- a/kernel/smp.c > +++ b/kernel/smp.c > @@ -791,6 +791,8 @@ static void smp_call_function_many_cond(const struct cpumask *mask, > } > } > > + if (!nr_cpus) > + goto local; Hmm, this isn't right. You can get nr_cpus==0 even though it did add some to various lists but never was first. But urgh, even if we were to say count nr_queued we'd never get the mask right, because we don't track which CPUs have the predicate matched, only those we need to actually send an IPI to :/ Ooh, I think we can clear those bits from cfd->cpumask, arguably that's a correctness fix too, because the 'run_remote && wait' case shouldn't wait on things we didn't queue. Hmm? --- a/kernel/smp.c +++ b/kernel/smp.c @@ -728,9 +728,9 @@ static void smp_call_function_many_cond( int cpu, last_cpu, this_cpu = smp_processor_id(); struct call_function_data *cfd; bool wait = scf_flags & SCF_WAIT; + int nr_cpus = 0, nr_queued = 0; bool run_remote = false; bool run_local = false; - int nr_cpus = 0; lockdep_assert_preemption_disabled(); @@ -772,8 +772,10 @@ static void smp_call_function_many_cond( for_each_cpu(cpu, cfd->cpumask) { call_single_data_t *csd = per_cpu_ptr(cfd->csd, cpu); - if (cond_func && !cond_func(cpu, info)) + if (cond_func && !cond_func(cpu, info)) { + __cpumask_clear_cpu(cpu, cfd->cpumask); continue; + } csd_lock(csd); if (wait) @@ -789,13 +791,15 @@ static void smp_call_function_many_cond( nr_cpus++; last_cpu = cpu; } + nr_queued++; } /* * Trace each smp_function_call_*() as an IPI, actual IPIs * will be traced with func==generic_smp_call_function_single_ipi(). */ - trace_ipi_send_cpumask(cfd->cpumask_ipi, _RET_IP_, func); + if (nr_queued) + trace_ipi_send_cpumask(cfd->cpumask, _RET_IP_, func); /* * Choose the most efficient way to send an IPI. Note that the