Messages in this thread | | | Date | Wed, 7 Mar 2018 11:47:11 +0000 | From | Patrick Bellasi <> | Subject | Re: [PATCH v5 1/4] sched/fair: add util_est on top of PELT |
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On 06-Mar 20:02, Peter Zijlstra wrote: > On Thu, Feb 22, 2018 at 05:01:50PM +0000, Patrick Bellasi wrote: > > +struct util_est { > > + unsigned int enqueued; > > + unsigned int ewma; > > +#define UTIL_EST_WEIGHT_SHIFT 2 > > +}; > > > + ue = READ_ONCE(p->se.avg.util_est); > > > + WRITE_ONCE(p->se.avg.util_est, ue); > > That is actually quite dodgy... and relies on the fact that we have the > 8 byte case in __write_once_size() and __read_once_size() > unconditionally. It then further relies on the compiler DTRT for 32bit > platforms, which is generating 2 32bit loads/stores. > > The advantage is of course that it will use single u64 loads/stores > where available.
Yes, that's mainly an "optimization" for 64bit targets... but perhaps the benefits are negligible.
Do you prefer to keep more "under control" the generated code by using two {READ,WRITE}_ONCEs?
IMO here we can also go with just the WRITE_ONCEs. I don't see a case for the compiler to mangle load/store. While the WRITE_ONCE are still required to sync with non rq-lock serialized code. But... maybe I'm missing something... ?
-- #include <best/regards.h>
Patrick Bellasi
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