Messages in this thread | | | Date | Mon, 26 Nov 2018 10:30:51 +0100 | From | Peter Zijlstra <> | Subject | Re: [Question] atomic_fetch_andnot() in nohz_idle_balance() |
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On Wed, Nov 21, 2018 at 11:34:53PM +0100, Andrea Parri wrote: > Hi, > > The comment for the atomic_fetch_andnot() in nohz_idle_balance() says: > > "barrier, pairs with nohz_balance_enter_idle(), ensures ..." > > which, well, does sound a note of warning... ;-) > > I see that nohz_balance_enter_idle() has an smp_mb__after_atomic() but > the comment for the latter suggests that this barrier is pairing with > the smp_mb() in _nohz_idle_balance(). > > So, what is the intended pairing barrier for the atomic_fetch_andnot()? > what (which memory accesses) do you want "to order" here?
I can't seem to make sense of that comment either; the best I can come up with is that it would order the prior NOHZ_KICK_MASK load vs us then changing it.
But that would order against kick_ilb(), not enter_idle.
Vincent?
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