Messages in this thread | | | Date | Thu, 13 Apr 2017 10:03:49 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH tip/core/rcu 02/40] rcu: Make arch select smp_mb__after_unlock_lock() strength |
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On Thu, Apr 13, 2017 at 06:37:57PM +0200, Peter Zijlstra wrote: > On Thu, Apr 13, 2017 at 09:26:51AM -0700, Paul E. McKenney wrote: > > > ARCH_WEAK_RELEASE_ACQUIRE actually works both ways. > > > > To see this, imagine some strange alternate universe in which the Power > > hardware guys actually did decide to switch PPC to doing RCsc as you > > suggest. There would still be a lot of Power hardware out there that > > still does RCpc. Therefore, powerpc builds that needed to run on old > > Power hardware would select ARCH_WEAK_RELEASE_ACQUIRE, while kernels > > built to run only on the shiny new (but mythical) alternate-universe > > Power hardware would avoid selecting this Kconfig option. > > Ah, but Power software guys could do it today by replacing an LWSYNC > with a SYNC in say arch_spin_unlock(). > > And yes, I know this isn't a popular suggestion, but it would do the > trick.
Indeed, there is a fine line between motivating people to move to new hardware on the one hand and terminally annoying existing users on the other. ;-)
> Its just that since there's one (PPC) we can sort of pressure them with > the pain of being the only ones to hit all the bugs. But the moment more > appear (and I'm afraid it'll be MIPS, with the excuse that PPC already > does this) it will be ever so much harder to get rid of it. > > Then again, maybe I should just give up and accept the Linux kernel has > RCpc locks..
As usual, I must defer to the powerpc maintainers on this one.
Thanx, Paul
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