Re: [RFC] Avoid mutex starvation when optimistic spinning is disabled

[Davidlohr Bueso]

On Fri, 22 Jul 2016, Imre Deak wrote:

> On Fri, 2016-07-22 at 11:03 -0700, Davidlohr Bueso wrote:
> > On Fri, 22 Jul 2016, Waiman Long wrote:
> >
> > > I think making mutex_trylock() fail maybe a bit too far. Do we
> > > really
> > > have any real workload that cause starvation problem  because of
> > > that.
> > > Code that does mutex_trylock() in a loop can certainly cause lock
> > > starvation, but it is not how mutex_trylock() is supposed to be
> > > used.
> > > We can't build in safeguard for all the possible abuses of the
> > > mutex
> > > APIs.
> >
> > True, and that's actually why I think that 'fixing' the
> > !SPIN_ON_OWNER case
> > is a bit too far in the first place: most of the archs that will care
> > about
> > this already have ARCH_SUPPORTS_ATOMIC_RMW. The extra code for
> > dealing with
> > this is not worth it imo.
>
> SPIN_ON_OWNER is also disabled in case of DEBUG_MUTEXES, which is the
> config where I wanted to avoid starvation in the first place.

Well yes, but know of course that that option is even less common than
archs with non atomic Rmw.

Thanks,
Davidlohr