Re: [Xen-devel] [PATCH v9 05/19] qspinlock: Optimize for smaller NR_CPUS

[Ingo Molnar <mingo@xxxxxxxxxx>]

* Waiman Long <waiman.long@xxxxxx> wrote:

> On 04/18/2014 03:46 AM, Ingo Molnar wrote:
> >* Waiman Long<waiman.long@xxxxxx>  wrote:
> >
> >>On 04/17/2014 11:58 AM, Peter Zijlstra wrote:
> >>>On Thu, Apr 17, 2014 at 11:03:57AM -0400, Waiman Long wrote:
> >>>>+static __always_inline void
> >>>>+clear_pending_set_locked(struct qspinlock *lock, u32 val)
> >>>>+{
> >>>>+ struct __qspinlock *l = (void *)lock;
> >>>>+
> >>>>+ ACCESS_ONCE(l->locked_pending) = 1;
> >>>>+}
> >>>>@@ -157,8 +251,13 @@ static inline int trylock_pending(struct qspinlock 
> >>>>*lock, u32 *pval)
> >>>>           * we're pending, wait for the owner to go away.
> >>>>           *
> >>>>           * *,1,1 ->   *,1,0
> >>>>+  *
> >>>>+  * this wait loop must be a load-acquire such that we match the
> >>>>+  * store-release that clears the locked bit and create lock
> >>>>+  * sequentiality; this because not all try_clear_pending_set_locked()
> >>>>+  * implementations imply full barriers.
> >>>You renamed the function referred in the above comment.
> >>>
> >>Sorry, will fix the comments.
> >I suggest not renaming the function instead.
> >try_clear_pending_set_locked() tells the intent in a clearer fashion.
> >
> >Thanks,
> >
> >     Ingo
> 
> I usually use the word "try" if there is a possibility of failure. 
> However, the function will always succeed, albeit by waiting a bit 
> in some cases. That is why I remove "try" from the name.

Fair enough!

Thanks,

        Ingo

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