Messages in this thread | | | Date | Fri, 11 Apr 2014 17:30:59 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC][PATCH 2/8] sched,idle,tile: Switch from TS_POLLING to TIF_POLLING_NRFLAG |
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On Fri, Apr 11, 2014 at 11:15:14AM -0400, Chris Metcalf wrote: > It's unfortunate that you're rolling the fetch_or() unconditionally > out of cmpxchg(), since some architectures (like tilegx) do have > support for "fetchor" as a primitive atomic operation. Currently the > tilegx fetchor is only exposed to architecture-independent code via > set_bit() and test_and_set_bit(), but perhaps it's worth having an > atomic_or() in atomic.h so architectures can choose to optimize it?
Yeah, I know.. Linus hated atomic_or_return() -- which admittedly is a little worse than fetch_or, because the operation isn't reversible.
Note that atomic_or_return() or rather, atomic_return_or() won't actually work here because thread_info::flags is not a fixed typed between archs, some have int, some have long.
Then again, when I proposed that thing, I didn't have a usage for it. Still, Linus' main argument still holds, its a crappy primitive on x86 and one should not encourage its use by pretending its 'easy'.
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