On Wed, 2016-08-31 at 09:18 +0200, Peter Zijlstra wrote: > On Wed, Aug 31, 2016 at 07:28:18AM +1000, Benjamin Herrenschmidt > wrote: > > > > It's always been a requirement that if you actually context switch > > a > > full mb() is implied ... > > > > > On powerpc we have a sync deep in _switch to achieve that. > > OK, fair enough. I must've missed it in the x86 switch_to, must be > one > of those implied serializing instructions I'm not too familiar with. > > > > > (though that isn't the case if you don't actually > > switch, ie, you are back to RUNNING before you even hit schedule). > > Right, which invalidates the claim that schedule() implies a full mb,
Right, it's only full mb if you actually schedule to another process :- ) > > > > This is necessary so that a process who wakes up on a different CPU > > sees > > all of its own load/stores. > > Don't actually think its needed for that, see the comment from > 8643cda549ca4, the scheduler has enough barriers to guarantee > Program-Order for tasks without that. >
