* Arjan van de Ven <[email protected]> wrote:
> > + * 1) if the exclusive store fails we fail, and
> > + *
> > + * 2) if the decremented value is not zero we don't even attempt the store.
>
>
> btw I really think that 1) is wrong. trylock should do everything it
> can to get the semaphore short of sleeping. Just because some
> cacheline got written to (which might even be shared!) in the middle
> of the atomic op is not a good enough reason to fail the trylock imho.
> Going into the slowpath.. fine. But here it's a quality of
> implementation issue; you COULD get the semaphore without sleeping (at
> least probably, you'd have to retry to know for sure) but because
> something wrote to the same cacheline as the lock... no. that's just
> not good enough.. sorry.
point. I solved this in my tree by calling the generic trylock <fn> if
there's an __ex_flag failure in the ARMv6 case. Should be rare (and thus
the call is under unlikely()), and should thus still enable the fast
implementation.
Ingo
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