Messages in this thread | | | From | David Howells <> | Subject | Re: [PATCH 03/10] rwsem: lighter active count checks when waking up readers | Date | Wed, 19 May 2010 13:25:31 +0100 |
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Michel Lespinasse <walken@google.com> wrote:
> ... When there are waiter threads on a rwsem and the spinlock is held, other > threads can only increment the active count by trying to grab the rwsem in > up_xxxx().
That's not true. A thread attempting to get an rwsem by issuing a down_read() or down_write() will also unconditionally increment the active count before it considers calling out to the slow path.
Maybe what you mean is that other threads wanting to do a wake up can only increase the active count for the processes being woken up whilst holding the rwsem's spinlock.
> + /* If we come here from up_xxxx(), another thread might have reached > + * rwsem_down_failed_common() before we acquired the spinlock and > + * woken up an active locker.
Do you mean a waiter rather than an active locker? If a process is still registering activity on the rwsem, then it can't be woken yet. Michel Lespinasse <walken@google.com> wrote:
> + * Note that we do not need to update the rwsem count: any writer > + * trying to acquire rwsem will run rwsem_down_write_failed() due > + * to the waiting threads, and block trying to acquire the spinlock.
That comma shouldn't be there.
> /* Grant an infinite number of read locks to the readers at the front > * of the queue. Note we increment the 'active part' of the count by
I wonder if I should've called it the 'activity part' of the count rather than the 'active part'.
Apart from that, the patch looks fine. That's all comment/description fixes.
David
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