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