On Friday 10 July 2015 12:35 PM, Peter Zijlstra wrote: > On Fri, Jul 10, 2015 at 04:30:46AM +0000, Vineet Gupta wrote: >> > >> > Since we are on the topic, the cmpxchg() loop in arch/arc/kernel/smp.c >> > still >> > irritates me. >> > Do we need a new set of primitives to operate atomically on non atomic_t >> > data or >> > does that mean that the data *not* being atomic_t but requiring such >> > semantics is >> > the fundamental problem and thus needs to be converted first. > So if you look at the last patch, there's already a few sites that do > things like: > > + atomic_or(*mask, (atomic_t *)&flushcache_cpumask); > > Which is of course ugly as hell, but does work. > > Esp. inside arch code.
Right - I don't have issues with using this API - but this requires atomic_t data type. The specific cmpxchg() loop that I'm referring to is not for atomic_t - so that needs to be converted to atomic_t first ? > > Now the 'problem' with cmpxchg/xchg, the instructions working on !atomic > data is: > > > http://lkml.kernel.org/r/alpine.lrh.2.02.1406011342470.20...@file01.intranet.prod.int.rdu2.redhat.com > > http://lkml.kernel.org/r/20140606175316.gv13...@laptop.programming.kicks-ass.net > > And note that includes some arc. Correct so we don't mix cmpxchg() with normal load/store. > > Adding more such primitives will only make it harder on those already > 'broken' archs. Not sure if I follow here - my point was not so much about expanding the atomic_*() API but whether it makes sense to have "some" API for non atomic_t vs. converting the non atomic_t to atomic_t and then use the API as that is the fundamental problem for such cases. -Vineet -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
