Messages in this thread | | | Date | Mon, 21 Mar 2022 13:32:27 +0000 | From | Will Deacon <> | Subject | Re: [PATCH 16/19] context_tracking: Convert state to atomic_t |
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On Sat, Mar 12, 2022 at 11:54:09PM +0100, Peter Zijlstra wrote: > On Wed, Mar 02, 2022 at 04:48:07PM +0100, Frederic Weisbecker wrote: > > +static __always_inline int __ct_state(void) > > +{ > > + return atomic_read(this_cpu_ptr(&context_tracking.state)); > > +} > > One arguably horrible thing to do would be to write it like: > > return __this_cpu_read(context_tracking.state.counter); > > IIRC that will actually DTRT since atomic_read() is basically defined to > be READ_ONCE() and this_cpu_read() implies the same. > > Only PowerPC and s390 implement arch_atomic_read() in asm, but I don't > think they have a particularly good reason to. The only other weird case > is Alpha, where READ_ONCE() implies smp_mb() because Alpha. I'm not sure > we care about that case, hmm?
If we don't care about the dependency ordering, then __READ_ONCE() is the chappy to use if the types don't get in the way too much.
Will
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