On Fri, 17 Jun 2016, Davidlohr Bueso wrote:
On Fri, 17 Jun 2016, Waiman Long wrote:On 06/16/2016 09:11 PM, Davidlohr Bueso wrote:On Wed, 15 Jun 2016, Peter Zijlstra wrote:Yeah, see a few patches further in this series, where he guards a variables with the osq_lock.So one problem I have with all this is that if we are hardening osq_lock/unlock() because of some future use that is specific to rwsems, then we will immediatelybe hurting mutexes for no good reason.I am going to change it to use smp_acquire__after_ctrl_dep() as suggested by PeterZ. Is that a good enough compromise? I have also changed the xchg in the unlock side to xchg_release which could help performance in some archs. The thing is when developers see the name osq_lock/osq_unlock, they will naturally assume the proper barrriers are provided which is not currently the case.Oh, from your discussions with Boqun, I was under the impression that ->locked was now going to be properly ordered in all cases now, which is why I worry about mutexes.Anyway, the change won't affect x86, it is probably ARM or PPC that may have an impact.Yes, that xchg() won't affect x86, but adding an smp_store_release(node->locked, 1) or such will obviously.
nm this last part, you're right, x86 smp_store_release is a nop. -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
|