rwsem: lighter active count checks when waking up readers
in [Kernel]
|
Prev: x86, mem-hotplug: update all PGDs for direct mapping and vmemmap mapping changes on 64bit.
Next: rwsem: let RWSEM_WAITING_BIAS represent any number of waiting threads
From: David Howells on 19 May 2010 08:30 Michel Lespinasse <walken(a)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(a)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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: David Howells on 21 May 2010 04:10
Michel Lespinasse <walken(a)google.com> wrote: > down_xxxx can increase the active count ... Not so much can, as does... Perhaps you need to qualify that. David -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |