Messages in this thread | | | Date | Thu, 31 Jan 2002 15:55:02 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH] 2.5.3 remove global semaphore_lock spin lock. |
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Bob Miller wrote: > > Below is a patch for i386 that replaces the global spin lock semaphore_lock, > with the rwlock_t embedded in the wait_queue_head_t in the struct semaphore. >
Looks sane. In practice, the speedup is unmeasurable, but...
> ... > + unsigned long flags; > + wq_write_lock_irqsave(&sem->wait.lock, flags); > - spin_lock_irq(&semaphore_lock);
I rather dislike spin_lock_irq(), because it's fragile (makes assumptions about the caller's state). But in this case, it's probably a reasonable micro-optimisation to not have to save the flags. Nobody should be calling down() with local interrupts disabled.
> ... > +/* > + * Same as __wake_up but called with the wait_queue_head_t lock held > + * in at least read mode. > + */ > +void __wake_up_locked(wait_queue_head_t *q, unsigned int mode, int nr) > +{ > + if (q) {
I don't think we need to test `q' here. It's a new function, and we don't need to support broken callers. So __wake_up_locked() can become a macro direct call to __wake_up_common().
> + __wake_up_common(q, mode, nr, 0);
This one breaks the camel's back :)
Let's un-inline __wake_up_common and EXPORT_SYMBOL it.
It'd be good if you could also verify that the code still works when the use-rwlocks-for-waitqueues option is turned on. (wait.h:USE_RW_WAIT_QUEUE_SPINLOCK)
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