Messages in this thread | | | Date | Thu, 15 Jan 2009 19:02:59 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] percpu: add optimized generic percpu accessors |
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* Andrew Morton <akpm@linux-foundation.org> wrote:
> On Thu, 15 Jan 2009 22:23:19 +0900 Tejun Heo <tj@kernel.org> wrote: > > > --- a/include/asm-generic/percpu.h > > +++ b/include/asm-generic/percpu.h > > @@ -80,4 +80,56 @@ extern void setup_per_cpu_areas(void); > > #define DECLARE_PER_CPU(type, name) extern PER_CPU_ATTRIBUTES \ > > __typeof__(type) per_cpu_var(name) > > > > +/* > > + * Optional methods for optimized non-lvalue per-cpu variable access. > > + * > > + * @var can be a percpu variable or a field of it and its size should > > + * equal char, int or long. percpu_read() evaluates to a lvalue and > > + * all others to void. > > + * > > + * These operations are guaranteed to be atomic w.r.t. preemption. > > + * The generic versions use plain get/put_cpu_var(). Archs are > > + * encouraged to implement single-instruction alternatives which don't > > + * require preemption protection. > > + */ > > +#ifndef percpu_read > > +# define percpu_read(var) \ > > + ({ \ > > + typeof(per_cpu_var(var)) __tmp_var__; \ > > + __tmp_var__ = get_cpu_var(var); \ > > + put_cpu_var(var); \ > > + __tmp_var__; \ > > + }) > > +#endif > > I wonder if the preempt_disable()/preempt_enable() in here actually > does anything useful on any architecture.
Provides "this is IRQ safe" and "this is preempt safe" semantics.
Ingo
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