On Tue, 2013-06-11 at 12:49 -0700, Paul E. McKenney wrote: > +config TICKET_LOCK_QUEUED > + bool "Dynamically switch between ticket and queued locking" > + depends on SMP > + default n > + ---help--- > + Enable dynamic switching between ticketlock and queued locking > + on a per-lock basis. This option will slow down low-contention > + acquisition and release very slightly (additional conditional > + in release path), but will provide more efficient operation at > + high levels of lock contention. High-contention operation will > + not be quite as efficient as would be a pure queued lock, but > + this dynamic approach consumes less memory than queud locks > + and also runs faster at low levels of contention. > + > + Say "Y" if you are running on a large system with a workload > + that is likely to result in high levels of contention. > + > + Say "N" if you are unsure. > + > +config TICKET_LOCK_QUEUED_SWITCH > + int "When to switch from ticket to queued locking" > + depends on TICKET_LOCK_QUEUED > + default 8 > + range 3 32 > + ---help--- > + Specify how many tasks should be spinning on the lock before > + switching to queued mode. Systems with low-latency memory/cache > + interconnects will prefer larger numbers, while extreme low-latency > + and real-time workloads will prefer a smaller number. Of course, > + extreme real-time workloads would be even happier if contention > + on the locks were reduced to the point that there was never any > + need for queued locking in the first place.
Are you sure real-time wants low numbers? I would think that real-time would want this off. This is just a way to help prevent cache ping ponging, but it adds to non-deterministic behavior. As I mentioned before, even though you fixed the thundering herd on setup, once the queue is set, then we will get a thundering herd of tasks trying to queue itself, and the task that was spinning the longest could very well become the one at the end of the FIFO. -- Steve > + > + Take the default if you are unsure. > diff --git a/kernel/Makefile b/kernel/Makefile -- 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/
