From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e1.ny.us.ibm.com (e1.ny.us.ibm.com [32.97.182.141]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "e1.ny.us.ibm.com", Issuer "Equifax" (verified OK)) by ozlabs.org (Postfix) with ESMTPS id 60C27B7D0C for ; Wed, 21 Apr 2010 23:50:26 +1000 (EST) Received: from d01relay05.pok.ibm.com (d01relay05.pok.ibm.com [9.56.227.237]) by e1.ny.us.ibm.com (8.14.3/8.13.1) with ESMTP id o3LDjKFH026639 for ; Wed, 21 Apr 2010 09:45:20 -0400 Received: from d01av01.pok.ibm.com (d01av01.pok.ibm.com [9.56.224.215]) by d01relay05.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id o3LDoL2A147190 for ; Wed, 21 Apr 2010 09:50:21 -0400 Received: from d01av01.pok.ibm.com (loopback [127.0.0.1]) by d01av01.pok.ibm.com (8.14.3/8.13.1/NCO v10.0 AVout) with ESMTP id o3LDoLe9010729 for ; Wed, 21 Apr 2010 09:50:21 -0400 Message-ID: <4BCF029B.1020805@linux.vnet.ibm.com> Date: Wed, 21 Apr 2010 08:50:19 -0500 From: Brian King MIME-Version: 1.0 To: michael@ellerman.id.au Subject: Re: [PATCH 1/1] powerpc: Ignore IPIs to offline CPUs References: <201004210154.o3L1sXaR001791@d01av04.pok.ibm.com> <12054.1271815478@neuling.org> <4BCE6DDC.4020902@linux.vnet.ibm.com> <1271856929.3832.46.camel@concordia> In-Reply-To: <1271856929.3832.46.camel@concordia> Content-Type: text/plain; charset=UTF-8 Cc: Michael Neuling , linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 04/21/2010 08:35 AM, Michael Ellerman wrote: > On Tue, 2010-04-20 at 22:15 -0500, Brian King wrote: >> On 04/20/2010 09:04 PM, Michael Neuling wrote: >>> In message <201004210154.o3L1sXaR001791@d01av04.pok.ibm.com> you wrote: >>>> >>>> Since there is nothing to stop an IPI from occurring to an >>>> offline CPU, rather than printing a warning to the logs, >>>> just ignore the IPI. This was seen while stress testing >>>> SMT enable/disable. >>> >>> This seems like a recipe for disaster. Do we at least need a >>> WARN_ON_ONCE? >> >> Actually we are only seeing it once per offlining of a CPU, >> and only once in a while. >> >> My guess is that once the CPU is marked offline fewer IPIs >> get sent to it since its no longer in the online mask. > > Hmm, right. Once it's offline it shouldn't get _any_ IPIs, AFAICS. > >> Perhaps we should be disabling IPIs to offline CPUs instead? > > You mean not sending them? We do: > > void smp_xics_message_pass(int target, int msg) > { > unsigned int i; > > if (target < NR_CPUS) { > smp_xics_do_message(target, msg); > } else { > for_each_online_cpu(i) { > if (target == MSG_ALL_BUT_SELF > && i == smp_processor_id()) > continue; > smp_xics_do_message(i, msg); > } > } > } > > So it does sound like the IPI was sent while the cpu was online (ie. > before pseries_cpu_disable(), but xics_migrate_irqs_away() has not > caused the IPI to be cancelled. > > Problem is I don't think we can just ignore the IPI. The IPI might have > been sent for a smp_call_function() which is waiting for the result, in > which case if we ignore it the caller will block for ever. > > I don't see how to fix it :/ Any objections to just removing the warning? Thanks, Brian -- Brian King Linux on Power Virtualization IBM Linux Technology Center