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=-13.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 E2DAAC433DF for ; Mon, 6 Jul 2020 17:06:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BC2CA217D8 for ; Mon, 6 Jul 2020 17:06:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1594055211; bh=8EZi7GgGgPPffu74raLQxqgFlZz10X6qFN6WvUpuQPo=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=QZ6teheLN6LyLxZ9iOfgrqy4btcwxbQe5Qge2dd5v2U4246EHL+A2I87+9Xe8v+AJ 2jXkVDeDa77i4Pk3rJ7R0oMIpJjWRAvrmtRhxaLPsJ2+adCHSaByhMzZ+P5LXe9Qv4 QciQcT4jLpa/Z/dFJE2yQi3Nh6IOqIuvjfEqQn0U= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729621AbgGFRGu (ORCPT ); Mon, 6 Jul 2020 13:06:50 -0400 Received: from mail.kernel.org ([198.145.29.99]:48880 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729568AbgGFRGu (ORCPT ); Mon, 6 Jul 2020 13:06:50 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-111-31.bvtn.or.frontiernet.net [50.39.111.31]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id A698F217D8; Mon, 6 Jul 2020 17:06:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1594055209; bh=8EZi7GgGgPPffu74raLQxqgFlZz10X6qFN6WvUpuQPo=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=AtdJrePdNXqZISymueTLPI0FO1PLWT/VBuWVdmUxxusAWhC6ZPqF4QHRI6VP2PG48 rJ4LF9WmeDTDmgrwN6mR2DLd1cMEPkBRZNtxUq8VJB00o/J5Z1Az+92xKN8gI92g8G YZivT1vHl8uf+lMtCBD1JR7llIeplXAx0bHbnzoQ= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 8E5A63521502; Mon, 6 Jul 2020 10:06:49 -0700 (PDT) Date: Mon, 6 Jul 2020 10:06:49 -0700 From: "Paul E. McKenney" To: Qian Cai Cc: fweisbec@gmail.com, tglx@linutronix.de, mingo@kernel.org, linux-kernel@vger.kernel.org, luto@kernel.org, kernel-team@fb.com Subject: Re: [PATCH tick-sched] Clarify "NOHZ: local_softirq_pending" warning Message-ID: <20200706170649.GW9247@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200626210506.GA27189@paulmck-ThinkPad-P72> <20200706164816.GA1299@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200706164816.GA1299@lca.pw> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 06, 2020 at 12:48:16PM -0400, Qian Cai wrote: > On Fri, Jun 26, 2020 at 02:05:06PM -0700, Paul E. McKenney wrote: > > Currently, can_stop_idle_tick() prints "NOHZ: local_softirq_pending HH" > > (where "HH" is the hexadecimal softirq vector number) when one or more > > non-RCU softirq handlers are still enablded when checking to stop the > > scheduler-tick interrupt. This message is not as enlightening as one > > might hope, so this commit changes it to "NOHZ tick-stop error: Non-RCU > > local softirq work is pending, handler #HH. > > > > Reported-by: Andy Lutomirski > > Signed-off-by: Paul E. McKenney > > CPU hotplug will sometimes trigger this warning on linux-next from NUMA > bare-metal which the commit makes it feel more like errors. One point of the change was to make it clear that this is an error. So success! ;-) > [ 267.734981] smpboot: CPU 42 is now offline > [ 267.991940] smpboot: Booting Node 2 Processor 42 APIC 0x29 > [ 267.998370] numa_add_cpu cpu 42 node 2: mask now 8-11,40-43 > [ 268.092380] ACPI: \_SB_.SCK0.C015: Found 2 idle states > [ 268.181917] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #282 > [ 268.190585] numa_remove_cpu cpu 1 node 0: mask now 0,2-3,32-35 > [ 268.194075] smpboot: CPU 1 is now offline > [ 268.415320] x86: Booting SMP configuration: > [ 268.420245] smpboot: Booting Node 0 Processor 1 APIC 0x2 > > # git clone https://github.com/cailca/linux-mm > # cd linux-mm; make > # ./random 4 (it just soft offline and online each CPU) > > The x86.config is also included there. This is only reproducible on x86 > so far. I must defer to Frederic and Andy on this one. But now that you mention it, I do see this on some of my runs, which are x86, but not bare metal. I clearly need to upgrade my console-log parsing. Thanx, Paul > > --- > > > > tick-sched.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > > index f0199a4..349a25a 100644 > > --- a/kernel/time/tick-sched.c > > +++ b/kernel/time/tick-sched.c > > @@ -927,7 +927,7 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) > > > > if (ratelimit < 10 && > > (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) { > > - pr_warn("NOHZ: local_softirq_pending %02x\n", > > + pr_warn("NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #%02x\n", > > (unsigned int) local_softirq_pending()); > > ratelimit++; > > }