Messages in this thread | | | Date | Fri, 18 Sep 2020 13:03:10 +0200 | From | peterz@infradea ... | Subject | Re: [RFC PATCH] locking/percpu-rwsem: use this_cpu_{inc|dec}() for read_count |
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On Fri, Sep 18, 2020 at 12:48:24PM +0200, Oleg Nesterov wrote:
> Of course, this assumes that atomic_t->counter underflows "correctly", just > like "unsigned int".
We're documented that we do. Lots of code relies on that.
See Documentation/atomic_t.txt TYPES
> But again, do we really want this?
I like the two counters better, avoids atomics entirely, some archs hare horridly expensive atomics (*cough* power *cough*).
I just tried to be clever and use a single u64 load (where possible) instead of two 32bit loads and got the sum vs split order wrong.
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