Messages in this thread | | | Date | Tue, 14 Apr 2009 10:18:17 -0700 | From | Andrew Morton <> | Subject | Re: [patch for 2.6.30 2/2] arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c: avoid cross-CPU interrupts |
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On Tue, 14 Apr 2009 18:21:36 +0930 Rusty Russell <rusty@rustcorp.com.au> wrote:
> 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 <rusty@rustcorp.com.au> > CC: Andrew Morton <akpm@linux-foundation.org> > > 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); > +}
Should it be exported?
It looks all racy against hotplug. What are the caller's responsibilities here?
<greps a bit>
any_online_cpu() could use cpumask_closest(), against (*mask & cpu_online_map).
I think all cpumask_any() call sites can be migrated to cpumask_closest() with, at worst, no benefit.
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