Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753498AbZDTC5p (ORCPT ); Sun, 19 Apr 2009 22:57:45 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752311AbZDTC5f (ORCPT ); Sun, 19 Apr 2009 22:57:35 -0400 Received: from vms173005pub.verizon.net ([206.46.173.5]:61012 "EHLO vms173005pub.verizon.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751479AbZDTC5e (ORCPT ); Sun, 19 Apr 2009 22:57:34 -0400 Date: Sun, 19 Apr 2009 22:57:24 -0400 (EDT) From: Len Brown X-X-Sender: lenb@localhost.localdomain To: akpm@linux-foundation.org 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 In-reply-to: <200904110617.n3B6HJ7W026502@imap1.linux-foundation.org> Message-id: References: <200904110617.n3B6HJ7W026502@imap1.linux-foundation.org> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-version: 1.0 Content-type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2496 Lines: 73 > From: Andrew Morton > > In drv_read(), check to see whether we can run the rdmsr() on the current > CPU. If so, do that. So smp_call_function_single() can avoid the IPI. > > Arguably, cpumask_any() should do this. > > Cc: Rusty Russell > Cc: Ingo Molnar > Cc: Venkatesh Pallipadi > Cc: Len Brown > Cc: Zhao Yakui > Cc: Dave Jones > Cc: Thomas Gleixner > Tested-by: Mike Galbraith > Cc: "Zhang, Yanmin" > Signed-off-by: Andrew Morton > > --- > > arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c | 17 +++++++++++++++-- > 1 file changed, 15 insertions(+), 2 deletions(-) > > diff -puN arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c~arch-x86-kernel-cpu-cpufreq-acpi-cpufreqc-avoid-cross-cpu-interrupts arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c > --- a/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c~arch-x86-kernel-cpu-cpufreq-acpi-cpufreqc-avoid-cross-cpu-interrupts > +++ 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? or B. optimize smp_call_function_single to beneift all users instead of just this customer. thanks, -Len Brown, Intel Open Source Technology Center -- 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/