[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [v3,11/41] mips: reuse asm-generic/barrier.h
On Fri, Jan 15, 2016 at 10:13:48AM +0100, Peter Zijlstra wrote: > On Fri, Jan 15, 2016 at 09:55:54AM +0100, Peter Zijlstra wrote: > > On Thu, Jan 14, 2016 at 01:29:13PM -0800, Paul E. McKenney wrote: > > > So smp_mb() provides transitivity, as do pairs of smp_store_release() > > > and smp_read_acquire(), > > > > But they provide different grades of transitivity, which is where all > > the confusion lays. > > > > smp_mb() is strongly/globally transitive, all CPUs will agree on the order. > > > > Whereas the RCpc release+acquire is weakly so, only the two cpus > > involved in the handover will agree on the order. > > And the stuff we're confused about is how best to express the difference > and guarantees of these two forms of transitivity and how exactly they > interact. Hoping my memory-barrier.txt patch helps here... > And smp_load_acquire()/smp_store_release() are RCpc because TSO archs > and PPC. the atomic*_{acquire,release}() are RCpc because PPC and > LOCK,UNLOCK are similarly RCpc because of PPC. > > Now we'd like PPC to stick a SYNC in either LOCK or UNLOCK so at least > the locks are RCsc again, but they resist for performance reasons but > waver because they don't want to be the ones finding all the nasty bugs > because they're the only one. I believe that the relevant proverb said something about starving to death between two bales of hay... ;-) > Now the thing I worry about, and still have not had an answer to is if > weakly ordered MIPS will end up being RCsc or RCpc for their locks if > they get implemented with SYNC_ACQUIRE and SYNC_RELEASE instead of the > current SYNC. It would be good to have better clarity on this, no two ways about it. Thanx, Paul _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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