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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 5B826C433EF for ; Tue, 8 Feb 2022 13:17:52 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4JtNq22483z3bTQ for ; Wed, 9 Feb 2022 00:17:50 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20201202 header.b=k2Mb2BQl; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=kernel.org (client-ip=2604:1380:4641:c500::1; helo=dfw.source.kernel.org; envelope-from=frederic@kernel.org; receiver=) Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20201202 header.b=k2Mb2BQl; dkim-atps=neutral Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4JtNpH6D57z301M for ; Wed, 9 Feb 2022 00:17:11 +1100 (AEDT) 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 dfw.source.kernel.org (Postfix) with ESMTPS id 5B686616D6; Tue, 8 Feb 2022 13:17:07 +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 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> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Frederic Weisbecker , Thomas Gleixner , linuxppc-dev@lists.ozlabs.org, Ingo Molnar , LKML Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" 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.