On Wed, May 22, 2013 at 07:24:38PM +0200, Maarten Lankhorst wrote:
> >> +static inline void ww_acquire_init(struct ww_acquire_ctx *ctx,
> >> + struct ww_class *ww_class)
> >> +{
> >> + ctx->task = current;
> >> + do {
> >> + ctx->stamp = atomic_long_inc_return(&ww_class->stamp);
> >> + } while (unlikely(!ctx->stamp));
> > I suppose we'll figure something out when this becomes a bottleneck. Ideally
> > we'd do something like:
> >
> > ctx->stamp = local_clock();
> >
> > but for now we cannot guarantee that's not jiffies, and I suppose that's a tad
> > too coarse to work for this.
> This might mess up when 2 cores happen to return exactly the same time, how do you choose a winner in that case?
> EDIT: Using pointer address like you suggested below is fine with me. ctx pointer would be static enough.
Right, but for now I suppose the 'global' atomic is ok, if/when we find
it hurts performance we can revisit. I was just spewing ideas :-)
> > Also, why is 0 special?
> Oops, 0 is no longer special.
>
> I used to set the samp directly on the lock, so 0 used to mean no ctx set.
Ah, ok :-)
> >> +static inline int __must_check ww_mutex_trylock_single(struct ww_mutex *lock)
> >> +{
> >> + return mutex_trylock(&lock->base);
> >> +}
> > trylocks can never deadlock they don't block per definition, I don't see the
> > point of the _single() thing here.
> I called it single because they weren't annotated into any ctx. I can drop the _single suffix though,
> but you'd still need to unlock with unlock_single, or we need to remove that distinction altogether,
> lose a few lockdep checks and only have a one unlock function.
Again, early.. monday.. would a trylock, even if successful still need
the ctx?
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