Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753840AbZDTD3o (ORCPT ); Sun, 19 Apr 2009 23:29:44 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752619AbZDTD3d (ORCPT ); Sun, 19 Apr 2009 23:29:33 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:49030 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752260AbZDTD3c (ORCPT ); Sun, 19 Apr 2009 23:29:32 -0400 Date: Sun, 19 Apr 2009 20:20:14 -0700 From: Andrew Morton To: Len Brown Cc: linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org, davej@redhat.com, efault@gmx.de, len.brown@intel.com, mingo@elte.hu, rusty@rustcorp.com.au, tglx@linutronix.de, venkatesh.pallipadi@intel.com, yakui.zhao@intel.com, yanmin_zhang@linux.intel.com Subject: Re: [patch for 2.6.30 2/2] arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c: avoid cross-CPU interrupts Message-Id: <20090419202014.9a511aa9.akpm@linux-foundation.org> In-Reply-To: References: <200904110617.n3B6HJ7W026502@imap1.linux-foundation.org> X-Mailer: Sylpheed 2.4.8 (GTK+ 2.12.5; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1955 Lines: 61 On Sun, 19 Apr 2009 22:57:24 -0400 (EDT) Len Brown wrote: > > > > +++ a/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c > > @@ -197,9 +197,22 @@ static void do_drv_write(void *_cmd) > > > > static void drv_read(struct drv_cmd *cmd) > > { > > - cmd->val = 0; > > + int target_cpu; /* The CPU on which to perform thr rdmsr() */ > > + int this_cpu; > > + > > + /* > > + * If the current CPU is in cmd->mask then run the rdmsr() on this > > + * CPU to avoid the cross-cpu interrupt. > > + */ > > + this_cpu = get_cpu(); > > + if (cpu_isset(this_cpu, *(cmd->mask))) > > + target_cpu = this_cpu; > > + else > > + target_cpu = cpumask_any(cmd->mask); > > > > - smp_call_function_single(cpumask_any(cmd->mask), do_drv_read, cmd, 1); > > + cmd->val = 0; > > + smp_call_function_single(target_cpu, do_drv_read, cmd, 1); > > + put_cpu(); > > } > > > > static void drv_write(struct drv_cmd *cmd) > > _ > > Rather than this patch I would expect we would want to either: > > A. as we went to the trouble to detect the local case > in drv_read, why call smp_call_function at all for that case? Sure, that would work. I felt it was a little cleaner to always delegate the call to smp_call_function() rather than open-coding smp_call_function()'s internal implementation details at this site. We'd need to do: local_irq_disable(); /* Because this is what smp_call_function_single() does */ do_drv_read(...); local_irq_enable(); > or > > B. optimize smp_call_function_single to beneift all users > instead of just this customer. Yep. That would be a new smp_call_function_any() which takes a cpumask rather than a single CPU number. I think Rusty was cooking something up.. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/