Messages in this thread | | | Date | Tue, 14 Jul 2015 11:16:59 +0100 | From | Will Deacon <> | Subject | Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() |
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On Mon, Jul 13, 2015 at 11:31:29PM +0100, Benjamin Herrenschmidt wrote: > On Mon, 2015-07-13 at 13:15 +0100, Will Deacon wrote: > > This didn't go anywhere last time I posted it, but here it is again. > > I'd really appreciate some feedback from the PowerPC guys, especially as > > to whether this change requires them to add an additional barrier in > > arch_spin_unlock and what the cost of that would be. > > We'd have to turn the lwsync in unlock or the isync in lock into a full > barrier. As it is, we *almost* have a full barrier semantic, but not > quite, as in things can get mixed up inside spin_lock between the LL and > the SC (things leaking in past LL and things leaking "out" up before SC > and then getting mixed up in there).
Thanks, Ben.
> Michael, at some point you were experimenting a bit with that and tried > to get some perf numbers of the impact that would have, did that > solidify ? Otherwise, I'll have a look when I'm back next week.
These numbers would be really interesting...
Will
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