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 49A8BC433F5 for ; Tue, 8 Feb 2022 13:23:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1355408AbiBHNXT (ORCPT ); Tue, 8 Feb 2022 08:23:19 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40686 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351396AbiBHNU0 (ORCPT ); Tue, 8 Feb 2022 08:20:26 -0500 Received: from sin.source.kernel.org (sin.source.kernel.org [IPv6:2604:1380:40e1:4800::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 704E0C03BFFA for ; Tue, 8 Feb 2022 05:17:10 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sin.source.kernel.org (Postfix) with ESMTPS id A8E5BCE182D for ; Tue, 8 Feb 2022 13:17:08 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3E9BFC004E1; Tue, 8 Feb 2022 13:17:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1644326226; bh=pyYWSe+Jjk7H9EMWk07P5RtmfXzKKM1LErV2wfS8qKg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=k2Mb2BQlgKuqbJaDUtjCkPOrmzwYLXU48ytWbBxEOlY5sBc9caCg1cY5DFmj+Q0Q5 VtQDkm/UyWabPnK13Y4FZilRsArQJb6LvzhbwSWxpiJofz2EMt42FvqfR2U4cXnqCn BTgXhYEtoXNWR8IrOUU7SihX8Nkj9aadSVugloSDB7u9GRd8Ffiz2k3PimkHOGfASe uJqt0eoPytb+fHeBNjqsLQglRLI37wL6wnK4bxiXNr0Mp1hwRGiAZQ1oKpM6tXESyA 097YSjs9s2skEMTczes+grTL11i90cg9DB8WePmZayo5N2tdxYiMkfWpn6ZkqSowYM KHZR/mL9ePDxw== Date: Tue, 8 Feb 2022 14:17:03 +0100 From: Frederic Weisbecker To: Paul Menzel Cc: Frederic Weisbecker , Thomas Gleixner , Ingo Molnar , LKML , linuxppc-dev@lists.ozlabs.org Subject: Re: ppc64le: `NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #20!!!` when turning off SMT Message-ID: <20220208131703.GA538566@lothringen> References: <0baca95b-771f-2217-1098-2d0eee568ea7@molgen.mpg.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <0baca95b-771f-2217-1098-2d0eee568ea7@molgen.mpg.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 08, 2022 at 08:32:37AM +0100, Paul Menzel wrote: > Dear Linux folks, > > > On the POWER8 server IBM S822LC running Ubuntu 21.10, Linux 5.17-rc1+ built > with > > $ grep HZ /boot/config-5.17.0-rc1+ > CONFIG_NO_HZ_COMMON=y > # CONFIG_HZ_PERIODIC is not set > CONFIG_NO_HZ_IDLE=y > # CONFIG_NO_HZ_FULL is not set > CONFIG_NO_HZ=y > # CONFIG_HZ_100 is not set > CONFIG_HZ_250=y > # CONFIG_HZ_300 is not set > # CONFIG_HZ_1000 is not set > CONFIG_HZ=250 > > once warned about a NOHZ tick-stop error, when I executed `sudo > /usr/sbin/ppc64_cpu --smt=off` (so that KVM would work). I see, so I assume this sets some CPUs offline, right? > > ``` > $ dmesg > [ 0.000000] Linux version 5.17.0-rc1+ > (pmenzel@flughafenberlinbrandenburgwillybrandt.molgen.mpg.de) (Ubuntu clang > version 13.0.0-2, LLD 13.0.0) #1 SMP Fri Jan 28 17:13:04 CET 2022 > […] > [271272.030262] NOHZ tick-stop error: Non-RCU local softirq work is pending, > handler #20!!! > [271272.305726] NOHZ tick-stop error: Non-RCU local softirq work is pending, > handler #20!!! > [271272.549790] NOHZ tick-stop error: Non-RCU local softirq work is pending, > handler #20!!! > [271274.885167] NOHZ tick-stop error: Non-RCU local softirq work is pending, > handler #20!!! > [271275.113896] NOHZ tick-stop error: Non-RCU local softirq work is pending, > handler #20!!! > [271275.412902] NOHZ tick-stop error: Non-RCU local softirq work is pending, > handler #20!!! > [271275.625245] NOHZ tick-stop error: Non-RCU local softirq work is pending, > handler #20!!! > [271275.833107] NOHZ tick-stop error: Non-RCU local softirq work is pending, > handler #20!!! > [271276.041391] NOHZ tick-stop error: Non-RCU local softirq work is pending, > handler #20!!! > [271277.244880] NOHZ tick-stop error: Non-RCU local softirq work is pending, > handler #20!!! > ``` That's IRQ_POLL_SOFTIRQ. The problem here is probably that some of these softirqs are pending even though ksoftirqd has been parked. I see there is irq_poll_cpu_dead() that migrates the pending queue once the CPU is finally dead, so this is well handled. I'm preparing a patch to fix the warning. Thanks.