From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754830AbaEOTgF (ORCPT ); Thu, 15 May 2014 15:36:05 -0400 Received: from e28smtp07.in.ibm.com ([122.248.162.7]:49280 "EHLO e28smtp07.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751453AbaEOTgD (ORCPT ); Thu, 15 May 2014 15:36:03 -0400 Message-ID: <537516DA.9010407@linux.vnet.ibm.com> Date: Fri, 16 May 2014 01:04:50 +0530 From: "Srivatsa S. Bhat" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120828 Thunderbird/15.0 MIME-Version: 1.0 To: Joe Perches CC: peterz@infradead.org, tglx@linutronix.de, mingo@kernel.org, tj@kernel.org, rusty@rustcorp.com.au, akpm@linux-foundation.org, fweisbec@gmail.com, hch@infradead.org, mgorman@suse.de, riel@redhat.com, bp@suse.de, rostedt@goodmis.org, mgalbraith@suse.de, ego@linux.vnet.ibm.com, paulmck@linux.vnet.ibm.com, oleg@redhat.com, rjw@rjwysocki.net, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 1/3] smp: Print more useful debug info upon receiving IPI on an offline CPU References: <20140515191218.19811.25887.stgit@srivatsabhat.in.ibm.com> <20140515191259.19811.81032.stgit@srivatsabhat.in.ibm.com> <1400181576.5058.19.camel@joe-AO725> In-Reply-To: <1400181576.5058.19.camel@joe-AO725> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14051519-8878-0000-0000-00000C727CD2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/16/2014 12:49 AM, Joe Perches wrote: > On Fri, 2014-05-16 at 00:43 +0530, Srivatsa S. Bhat wrote: >> Today the smp-call-function code just prints a warning if we get an IPI on >> an offline CPU. This info is sufficient to let us know that something went >> wrong, but often it is very hard to debug exactly who sent the IPI and why, >> from this info alone. > [] >> diff --git a/kernel/smp.c b/kernel/smp.c > [] >> @@ -185,14 +185,26 @@ void generic_smp_call_function_single_interrupt(void) > [] >> - entry = llist_del_all(&__get_cpu_var(call_single_queue)); >> - entry = llist_reverse_order(entry); >> + /* >> + * We don't have to use the _safe() variant here >> + * because we are not invoking the IPI handlers yet. >> + */ >> + llist_for_each_entry(csd, entry, llist) >> + pr_warn("IPI callback %pS sent to offline CPU\n", >> + csd->func); > > Perhaps add ratelimited? > This entire scenario is expected to be _very_ infrequent, and even if it happens, these prints will appear only once during the entire run (note the use of the 'warned' variable to control that). So I don't think ratelimiting is called for in this case. Regards, Srivatsa S. Bhat