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SubjectRe: [PATCH] rwsem: reduce spinlock contention in wakeup code path
On Tue, Oct 01, 2013 at 09:28:15AM +0200, Ingo Molnar wrote:
> That I mostly agree with, except that without a serious usecase do we have
> a guarantee that bugs in fancies queueing in rwsems gets ironed out?

Methinks mmap_sem is still a big enough lock to work out a locking
primitive :-)

In fact, try something like this from userspace:

n-threads:

pthread_mutex_lock(&mutex);
foo = mmap();
pthread_mutex_lock(&mutex);

/* work */

pthread_mutex_unlock(&mutex);
munma(foo);
pthread_mutex_unlock(&mutex);

vs

n-threads:

foo = mmap();
/* work */
munmap(foo);


I've had reports that the former was significantly faster than the
latter.


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