From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rusty Russell Subject: Re: [patch for 2.6.30 2/2] arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c: avoid cross-CPU interrupts Date: Tue, 14 Apr 2009 18:21:36 +0930 Message-ID: <200904141821.37413.rusty@rustcorp.com.au> References: <200904110617.n3B6HJ7W026502@imap1.linux-foundation.org> <20090412000605.GA23869@redhat.com> <20090411174644.ea6f63c6.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Return-path: Received: from ozlabs.org ([203.10.76.45]:52091 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751040AbZDNIvt (ORCPT ); Tue, 14 Apr 2009 04:51:49 -0400 In-Reply-To: <20090411174644.ea6f63c6.akpm@linux-foundation.org> Content-Disposition: inline Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Andrew Morton Cc: Dave Jones , lenb@kernel.org, linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org, efault@gmx.de, len.brown@intel.com, mingo@elte.hu, tglx@linutronix.de, venkatesh.pallipadi@intel.com, yakui.zhao@intel.com, yanmin_zhang@linux.intel.com On Sun, 12 Apr 2009 10:16:44 am Andrew Morton wrote: > I suspect that changing cpumask_any() to preferentially return this-cpu > will always give us the behaviour that we prefer, but I haven't looked > into it. How's this? Subject: cpumask: cpumask_closest() Impact: new function Andrew points out that acpi-cpufreq uses cpumask_any, when it really would prefer to use the same CPU if possible (to avoid an IPI). In general, this seems a good idea to offer. Signed-off-by: Rusty Russell CC: Andrew Morton diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h --- a/include/linux/cpumask.h +++ b/include/linux/cpumask.h @@ -931,6 +931,8 @@ static inline void cpumask_copy(struct c */ #define cpumask_of(cpu) (get_cpu_mask(cpu)) +unsigned int cpumask_closest(const struct cpumask *mask); + /** * cpumask_scnprintf - print a cpumask into a string as comma-separated hex * @buf: the buffer to sprintf into diff --git a/lib/cpumask.c b/lib/cpumask.c --- a/lib/cpumask.c +++ b/lib/cpumask.c @@ -170,3 +170,26 @@ void __init free_bootmem_cpumask_var(cpu free_bootmem((unsigned long)mask, cpumask_size()); } #endif + +/** + * cpumask_closest - return the closest cpu in mask. + * @mask: the cpus to choose from. + * + * Returns >= nr_cpu_ids if no bits are set in @mask. + */ +unsigned int cpumask_closest(const struct cpumask *mask) +{ + unsigned int cpu = raw_smp_processor_id(); + + /* Try for same CPU. */ + if (cpumask_test_cpu(cpu, mask)) + return cpu; + + /* Try for same node. */ + cpu = cpumask_any_and(cpumask_of_node(cpu), mask); + if (cpu <= nr_cpu_ids) + return cpu; + + /* Anything will do. */ + return cpumask_any(mask); +}