Nick Piggin <[EMAIL PROTECTED]> writes: > I made some tests of the queued spinlock code using userspace test code on > 64-bit processors. I believe the xadd based code no longer has any theoretical > memory ordering problems.
Linus, the background of this is that on 8 socket Opteron systems the current spinlocks can become very unfair to the point of severe starvation. These boxes are becomming more common. > The threaded results also attempt to have an unfairness count, which is the > max number of times in a row that a lock is acquired, when all other threads > are also executing in the loop -- the reason xadd for example is not always > 0 there is because the other threads may not have reached the lock before > the current thread was able to get it several times (eg. if an interrupt > comes in, this could happen). Interesting. I was also thinking about switching the lock types at boot time. Since all the lock calls are out of line this would be reasonably easy. I would say the main drawback of switchable and queued locks would be also that they require a larger spinlock_t thus increasing cache usage e.g. it would probably hurt for the large spinlock tables used by TCP, but then those should be fixed anyways to be smaller. -Andi - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
