On Tue, Sep 10, 2013 at 07:02:51AM -0700, Eric Dumazet wrote:
> On Tue, 2013-09-10 at 15:08 +0200, Peter Zijlstra wrote:
>
> > +static __always_inline int preempt_count(void)
> > +{
> > + return __this_cpu_read_4(__preempt_count) & ~PREEMPT_NEED_RESCHED;
> > +}
>
> Not sure why you used the _4 prefix on all accessors ?
Last time I tried using the proper this_cpu* stuff that all exploded in
my face due to header recursion hell, so I've limited myself to what's
available in arch/x86/include/asm/percpu.h.
It was a few weeks ago though and maybe I just didn't try hard enough.
> > +#ifdef CONFIG_PREEMPT_COUNT
> > + /*
> > + * If it were not for PREEMPT_ACTIVE we could guarantee that the
> > + * preempt_count of all tasks was equal here and this would not be
> > + * needed.
> > + */
> > + task_thread_info(prev_p)->saved_preempt_count = __raw_get_cpu_var(__preempt_count);
>
> this_cpu_read(__preempt_count) ?
>
> > + __raw_get_cpu_var(__preempt_count) = task_thread_info(next_p)->saved_preempt_count;
>
> this_cpu_write(__preempt_count,
> task_thread_info(next_p)->saved_preempt_count;
OK, that does indeed generate slightly better code.
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