On 01/09/16 07:47, Benjamin Herrenschmidt wrote: > On Wed, 2016-08-31 at 15:31 +0200, Peter Zijlstra wrote: >> On Wed, Aug 31, 2016 at 07:28:18AM +1000, Benjamin Herrenschmidt >> wrote: >> >>> >>> On powerpc we have a sync deep in _switch to achieve that. >> >> OK, for giggles, could you (or Balbir) check what happens if you take >> that sync out? >> >> There should be enough serialization in the generic code to cover the >> case that code mentions. >> >> ARM64 has a stronger barrier in its context switch code, but that's >> because they need to sync against external agents (like their TLB and >> cache) and no amount of generic locking is going to cover that. > > The problem is no amount of testing can tell you it works for sure :-) > > I would be nervous not having a real full sync in _switch. All we have > along the scheduler path is lwsync's and our isync based load construct > for spin_lock, I'm not sure what other assumptions we have around that > sync in there... >
I would agree, I am not sure of the assumptions either. Balbir Singh.