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SubjectRe: [PATCH v2] rwsem: Support optimistic spinning
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On Wed, 2014-04-30 at 14:06 -0700, Davidlohr Bueso wrote:

> > > > >
> > > > > if (count == RWSEM_WAITING_BIAS)
> > > > > old = cmpxchg(&sem->count, count, count + RWSEM_ACTIVE_BIAS);
> > > > > else
> > > > > old = cmpxchg(&sem->count, count, count + RWSEM_ACTIVE_WRITE_BIAS);
> > > >
> > > > I think I simply mis-typed it; shouldn't both cases be
> > > > RWSEM_ACTIVE_WRITE_BIAS ?
> > >
> > > Yeah, we should just write it as
> > > old = cmpxchg(&sem->count, count, RWSEM_ACTIVE_WRITE_BIAS);
> >
> > Oops, I mean
> > old = cmpxchg(&sem->count, count, count + RWSEM_ACTIVE_WRITE_BIAS);
> >
> > for count == 0, we need sem->count to be RWSEM_ACTIVE_WRITE_BIAS,
> > for count == RWSEM_WAITING_BIAS, we need sem->count to be RWSEM_WAITING_BIAS + RWSEM_ACTIVE_WRITE_BIAS
>
> Yep, I had just noticed this. Peter's original suggestion was correct,
> just needed to change RWSEM_ACTIVE_BIAS for RWSEM_ACTIVE_WRITE_BIAS.
>

Yes, I think we are all on the same page now.

Tim



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