From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757391AbYAJAbK (ORCPT ); Wed, 9 Jan 2008 19:31:10 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754304AbYAJAa5 (ORCPT ); Wed, 9 Jan 2008 19:30:57 -0500 Received: from mga03.intel.com ([143.182.124.21]:60354 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753919AbYAJAa4 convert rfc822-to-8bit (ORCPT ); Wed, 9 Jan 2008 19:30:56 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.24,264,1196668800"; d="scan'208";a="363019828" X-MimeOLE: Produced By Microsoft Exchange V6.5 Content-class: urn:content-classes:message MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT Subject: RE: [PATCH] Kick CPUS that might be sleeping in cpus_idle_wait Date: Wed, 9 Jan 2008 16:12:23 -0800 Message-ID: <924EFEDD5F540B4284297C4DC59F3DEE554130@orsmsx423.amr.corp.intel.com> In-Reply-To: <1199911330.975.3.camel@localhost.localdomain> X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: [PATCH] Kick CPUS that might be sleeping in cpus_idle_wait Thread-Index: AchTAMulN41K/Qv0Qn6o6r2yA3G1fgAGog+A References: <1199759244.26343.35.camel@localhost.localdomain> <20080108033329.GI2998@bingen.suse.de> <1199911330.975.3.camel@localhost.localdomain> From: "Pallipadi, Venkatesh" To: "Steven Rostedt" , "LKML" Cc: "Linus Torvalds" , "Andrew Morton" , "Ingo Molnar" , "Thomas Gleixner" , "Brown, Len" , "Adam Belay" , "Peter Zijlstra" , "Andi Kleen" X-OriginalArrivalTime: 10 Jan 2008 00:11:33.0625 (UTC) FILETIME=[5B9D4690:01C8531D] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >-----Original Message----- >From: Steven Rostedt [mailto:rostedt@goodmis.org] >Sent: Wednesday, January 09, 2008 12:42 PM >To: LKML >Cc: Linus Torvalds; Andrew Morton; Ingo Molnar; Thomas >Gleixner; Brown, Len; Pallipadi, Venkatesh; Adam Belay; Peter >Zijlstra; Andi Kleen >Subject: [PATCH] Kick CPUS that might be sleeping in cpus_idle_wait > >This patch is different than the first patch I sent out. >This one just sends an IPI to all CPUS that don't check in after 1 sec. > > >Sometimes cpu_idle_wait gets stuck because it might miss CPUS that are >already in idle, have no tasks waiting to run and have no interrupts >going to them. This is common on bootup when switching cpu idle >governors. > >This patch gives those CPUS that don't check in an IPI kick. > I think your RFC patch is the right solution here. As I see it, there is no race with your RFC patch. As long as you call a dummy smp_call_function on all CPUs, we should be OK. We can get rid of cpu_idle_state and the current wait forever logic altogether with dummy smp_call_function. And so there wont be any wait forever scenario. The whole point of cpu_idle_wait() is to make all CPUs come out of idle loop atleast once. The caller will use cpu_idle_wait something like this. // Want to change idle handler - Switch global idle handler to always present default_idle - call cpu_idle_wait so that all cpus come out of idle for an instant and stop using old idle pointer and start using default idle - Change the idle handler to a new handler - optional cpu_idle_wait if you want all cpus to start using the new handler immediately. May be the below 1s patch is safe bet for .24. But for .25, I would say we just replace all complicated logic by simple dummy smp_call_function and remove cpu_idle_state altogether. Thanks, Venki >Signed-off-by: Steven Rostedt >--- > arch/x86/kernel/process_32.c | 11 +++++++++++ > arch/x86/kernel/process_64.c | 11 +++++++++++ > 2 files changed, 22 insertions(+) > >Index: linux-compile-i386.git/arch/x86/kernel/process_32.c >=================================================================== >--- linux-compile-i386.git.orig/arch/x86/kernel/process_32.c >2008-01-09 14:09:36.000000000 -0500 >+++ linux-compile-i386.git/arch/x86/kernel/process_32.c >2008-01-09 14:09:45.000000000 -0500 >@@ -204,6 +204,10 @@ void cpu_idle(void) > } > } > >+static void do_nothing(void *unused) >+{ >+} >+ > void cpu_idle_wait(void) > { > unsigned int cpu, this_cpu = get_cpu(); >@@ -228,6 +232,13 @@ void cpu_idle_wait(void) > cpu_clear(cpu, map); > } > cpus_and(map, map, cpu_online_map); >+ /* >+ * We waited 1 sec, if a CPU still did not call idle >+ * it may be because it is in idle and not waking up >+ * because it has nothing to do. >+ * Give all the remaining CPUS a kick. >+ */ >+ smp_call_function_mask(map, do_nothing, 0, 0); > } while (!cpus_empty(map)); > > set_cpus_allowed(current, tmp); >Index: linux-compile-i386.git/arch/x86/kernel/process_64.c >=================================================================== >--- linux-compile-i386.git.orig/arch/x86/kernel/process_64.c >2008-01-09 14:09:36.000000000 -0500 >+++ linux-compile-i386.git/arch/x86/kernel/process_64.c >2008-01-09 15:17:20.000000000 -0500 >@@ -135,6 +135,10 @@ static void poll_idle (void) > cpu_relax(); > } > >+static void do_nothing(void *unused) >+{ >+} >+ > void cpu_idle_wait(void) > { > unsigned int cpu, this_cpu = get_cpu(); >@@ -160,6 +164,13 @@ void cpu_idle_wait(void) > cpu_clear(cpu, map); > } > cpus_and(map, map, cpu_online_map); >+ /* >+ * We waited 1 sec, if a CPU still did not call idle >+ * it may be because it is in idle and not waking up >+ * because it has nothing to do. >+ * Give all the remaining CPUS a kick. >+ */ >+ smp_call_function_mask(map, do_nothing, 0, 0); > } while (!cpus_empty(map)); > > set_cpus_allowed(current, tmp); > > >