Re: [PATCH 3/3] ring-buffer: add design document

Steven Rostedt
2009-06-11T01:58:15Z

On Thu, 11 Jun 2009, Huang Ying wrote:

> On Thu, 2009-06-11 at 03:53 +0800, Steven Rostedt wrote:
> > +
> > +cmpxchg - hardware assisted atomic transaction that performs the following:
> > +
> > + A = B iff previous A == C
> > +
> > + R = cmpxchg(A, C, B) is saying that we replace A with B if and only if
> > + current A is equal to C, and we put the old (current) A into R
> > +
> > + R gets the previous A regardless if A is updated with B or not.
> > +
> > + To see if the update was successful a compare of R == C may be used.
>
> As far as I know, some architectures have no hardware assisted (NMI
> safe) cmpxchg. Is it OK to use cmpxchg in architecture-independent code?

I can fall back to the lock solution for those archs without cmpxchg. It
is NMI safe, because we do spin_trylock() in NMI context. If we fail to
acquire the lock in NMI context, we simply drop the packet.

Are these archs without cmpxchg and NMIs, a concern for you?

-- Steve