On Tue, Jun 03, 2008 at 02:33:11PM +1000, Nick Piggin wrote: > On Monday 02 June 2008 19:56, Jes Sorensen wrote: > > Jeremy Higdon wrote: > > > We don't actually have that problem on the Altix. All writes issued > > > by CPU X will be ordered with respect to each other. But writes by > > > CPU X and CPU Y will not be, unless an mmiowb() is done by the > > > original CPU before the second CPU writes. I.e. > > > > > > CPU X writel > > > CPU X writel > > > CPU X mmiowb > > > > > > CPU Y writel > > > ... > > > > > > Note that this implies some sort of locking. Also note that if in > > > the above, CPU Y did the mmiowb, that would not work. > > > > Hmmm, > > > > Then it's less bad than I thought - my apologies for the confusion. > > > > Would we be able to use Ben's trick of setting a per cpu flag in > > writel() then and checking that in spin unlock issuing the mmiowb() > > there if needed? > > Yes you could, but your writels would still not be strongly ordered > within (or outside) spinlock regions, which is what Linus wants (and > I kind of agree with).
Yes they would be. Writes from the same CPU are always ordered. Writes from different CPUs are not, but that's only a concern if you protect writing via some sort of lock. If the lock release forces a barrier, that should take care of the problem. jeremy _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
