Messages in this thread | | | Date | Mon, 23 Sep 2013 10:50:17 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH] hotplug: Optimize {get,put}_online_cpus() |
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On Thu, 19 Sep 2013 16:32:41 +0200 Peter Zijlstra <peterz@infradead.org> wrote:
> +extern void __get_online_cpus(void); > + > +static inline void get_online_cpus(void) > +{ > + might_sleep(); > + > + preempt_disable(); > + if (likely(!__cpuhp_writer || __cpuhp_writer == current)) > + this_cpu_inc(__cpuhp_refcount); > + else > + __get_online_cpus(); > + preempt_enable(); > +}
This isn't much different than srcu_read_lock(). What about doing something like this:
static inline void get_online_cpus(void) { might_sleep();
srcu_read_lock(&cpuhp_srcu); if (unlikely(__cpuhp_writer || __cpuhp_writer != current)) { srcu_read_unlock(&cpuhp_srcu); __get_online_cpus(); current->online_cpus_held++; } }
static inline void put_online_cpus(void) { if (unlikely(current->online_cpus_held)) { current->online_cpus_held--; __put_online_cpus(); return; }
srcu_read_unlock(&cpuhp_srcu); }
Then have the writer simply do:
__cpuhp_write = current; synchronize_srcu(&cpuhp_srcu);
<grab the mutex here>
-- Steve
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