Messages in this thread | | | Date | Fri, 10 Jul 2015 09:05:11 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC][PATCH 02/24] arc: Provide atomic_{or,xor,and} |
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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.
Now the 'problem' with cmpxchg/xchg, the instructions working on !atomic data is:
http://lkml.kernel.org/r/alpine.LRH.2.02.1406011342470.20831@file01.intranet.prod.int.rdu2.redhat.com http://lkml.kernel.org/r/20140606175316.GV13930@laptop.programming.kicks-ass.net
And note that includes some arc.
Adding more such primitives will only make it harder on those already 'broken' archs.
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