On Thu, Nov 24, 2016 at 12:52:25PM +0100, Daniel Vetter wrote: > On Thu, Nov 24, 2016 at 12:40 PM, Peter Zijlstra <peterz at infradead.org> > wrote: > > > >> I do believe we can win a bit by keeping the wait list sorted, if we also > >> make sure that waiters don't add themselves in the first place if they see > >> that a deadlock situation cannot be avoided. > >> > >> I will probably want to extend struct mutex_waiter with ww_mutex-specific > >> fields to facilitate this (i.e. ctx pointer, perhaps stamp as well to > >> reduce > >> pointer-chasing). That should be fine since it lives on the stack. > > > > Right, shouldn't be a problem I think. > > > > The only 'problem' I can see with using that is that its possible to mix > > ww and !ww waiters through ww_mutex_lock(.ctx = NULL). This makes the > > list order somewhat tricky. > > > > Ideally we'd remove that feature, although I see its actually used quite > > a bit :/ > > I guess we could create a small fake acquire_ctx for single-lock > paths. That way callers still don't need to deal with having an > explicit ctx, but we can assume the timestamp (for ensuring fairness) > is available for all cases. Otherwise there's indeed a problem with > correctly (well fairly) interleaving ctx and non-ctx lockers I think.
Actually tried that, but we need a ww_class to get a stamp from, and ww_mutex_lock() doesn't have one of those..
