On Friday, December 04, 2015 11:41:01 AM Viresh Kumar wrote: > On 04-12-15, 02:18, Rafael J. Wysocki wrote: > > > + shared->skip_work--; > > > > Is there any reason for incrementing and decrementing this instead of > > setting > > it to either 0 or 1 (or maybe either 'true' or 'false' for that matter)? > > > > If my reading of the patch is correct, it can only be either 0 or 1 anyway, > > right? > > No. It can be 0, 1 or 2. > > If the timer handler is running on any CPU, we increment skip_work, so > its value is 1. If at the same time, we try to stop the governor, we > increment it again and its value is 2 now. > > Once timer-handler finishes, it decrements it and its value become 1. > Which guarantees that no other timer handler starts executing at this > point of time and we can safely do gov_cancel_timers(). And once we > are sure that we don't have any work/timer left, we make it 0 (as we > aren't sure of the current value, which can be 0 (if the timer handler > wasn't running when we stopped the governor) or 1 (if the timer > handler was running while stopping the governor)). > > Hope this clarifies it.
Well, almost, but not quite yet, because now the question is what prevents gov_cancel_work() from racing with dbs_work_handler(). If you can guarantee that they'll never run in parallel with each other, you probably don't need the whole counter dance. Otherwise, dbs_work_handler() should decrement the counter under the spinlock after all I suppose. Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
