On Mon, Dec 16, 2013 at 1:32 PM, John Stultz <john.stu...@linaro.org> wrote: > RT_MUTEXES can be configured out of the kernel, causing compile > problems with ION. > > Since there is no documentation as to why directly using rt_mutexes > is necessary (and very few drivers directly use rt_mutexes), simply > convert the ion_heap lock to a normal mutex.
rt_mutexes were added with the deferred freeing feature. Heaps need to return zeroed memory to userspace, but zeroing the memory on every allocation was causing performance issues. We added a SCHED_IDLE thread to zero memory in the background after freeing, but locking the heap from the SCHED_IDLE thread might block a high priority allocation thread for a long time. The lock is only used to protect the heap's free_list and free_list_size members, and is not held for any long or sleeping operations. Converting to a spinlock should prevent priority inversion without using the rt_mutex. I'd also rename it to free_lock to so it doesn't get used as a general heap lock. -- 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/
