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=-11.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 29FFBC433DF for ; Mon, 6 Jul 2020 16:48:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F3771206CD for ; Mon, 6 Jul 2020 16:48:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lca.pw header.i=@lca.pw header.b="UIQ7MwSs" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729547AbgGFQsY (ORCPT ); Mon, 6 Jul 2020 12:48:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49316 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729441AbgGFQsY (ORCPT ); Mon, 6 Jul 2020 12:48:24 -0400 Received: from mail-qv1-xf41.google.com (mail-qv1-xf41.google.com [IPv6:2607:f8b0:4864:20::f41]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 05D2CC061755 for ; Mon, 6 Jul 2020 09:48:24 -0700 (PDT) Received: by mail-qv1-xf41.google.com with SMTP id h18so17500471qvl.3 for ; Mon, 06 Jul 2020 09:48:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=lca.pw; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=2JeP+ifXxK0uosoL0t3ljC8p7SwsLP3wIIhTZzlV8qA=; b=UIQ7MwSsHnew0rf3x2kYsf185a4CnXXLIzbGGEkIBIJLsIGkSaCxq0wgwcvZgfDoPC GdfKnajsjzpi58T46CiEZJFlcZyXOsLW2KDeK1OEpSIRo+xc/lhBZdwX4jofnh/e2bcl 7b7Ggl9dwW1WGQoQinPG70YCIB2Py0+Xj6ydRKSz5AxYZvOa60hLvpgJilS20aXu+M8i OPAIAno7NjKP1z0oJ14HHuKv9wLLrCiJ8T/L5C3CUN6OsSL/4UFiICGb8g1i4Al/cmda c71xomgv3vK/OnxxOPY+ljqKj02oxpAXuJO6IrEPVmoFlkB+I/45NGkPaA/uJ4AZWLQU iTCA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=2JeP+ifXxK0uosoL0t3ljC8p7SwsLP3wIIhTZzlV8qA=; b=mek1MZGgp2uiq2o0mygkAWUdYEIHmEv7+Ux0Z7tQ42sIydfiIgnYOto/Ci+G4412L9 GKZIw2azeIBWMkT8wfQOgJUckgtFR9yielTgM8qVDKuMy+mxteMcFPh2f4Ihw/oVaP2Q A2pamj6FxCFehyjIVB8eZA6RvZMIyp6Jisd/ksOiH2clEXZ8SIZmQL2Kx67lwNWBw1Gy aT8APKu44PpcSedkVCJiFt3AuyjxCF/KhHYZnLL2vaVXuHjxJHxXWKfq8bNM1u28hfpM Wp7e2m+nrwVquSjKNuT+HxTYQWHmvwIy2Rpq/UnRseuUwrWJFR+w4WfCt2sgfyEX7c0w onNg== X-Gm-Message-State: AOAM531Zt5W3RJeFUUISbOj4TCLL1a6aGQwtbiVGr1mHdiO8S9KISkH4 xk48B3vTtnHSOvdTDhZK7k6Seg== X-Google-Smtp-Source: ABdhPJzAUyC3KmVI5dUsMpVXDC7KjcBlVki2JUxLLotxbYe6lInEGwUWM3CF8YkAEIdOaDn62P7GDg== X-Received: by 2002:a05:6214:72c:: with SMTP id c12mr45236733qvz.76.1594054103236; Mon, 06 Jul 2020 09:48:23 -0700 (PDT) Received: from lca.pw (pool-71-184-117-43.bstnma.fios.verizon.net. [71.184.117.43]) by smtp.gmail.com with ESMTPSA id 188sm19346978qkf.50.2020.07.06.09.48.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 06 Jul 2020 09:48:22 -0700 (PDT) Date: Mon, 6 Jul 2020 12:48:16 -0400 From: Qian Cai To: "Paul E. McKenney" 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: <20200706164816.GA1299@lca.pw> References: <20200626210506.GA27189@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200626210506.GA27189@paulmck-ThinkPad-P72> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. [ 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. > > --- > > 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++; > }