I need some time to understand your test examples. However, On 01/14/2016 12:34 PM, Paul E. McKenney wrote:
The WRC+addr+addr is OK because data dependencies are not required to be transitive, in other words, they are not required to flow from one CPU to another without the help of an explicit memory barrier.
I don't see any reliable way to fit WRC+addr+addr into "DATA DEPENDENCY BARRIERS" section recommendation to have data dependency barrier between read of a shared pointer/index and read the shared data based on that pointer. If you have this two reads, it doesn't matter the rest of scenario, you should put the dependency barrier in code anyway. If you don't do it in WRC+addr+addr scenario then after years it can be easily changed to different scenario which fits some of scenario in "DATA DEPENDENCY BARRIERS" section and fails.
Transitivity is
Peter Zijlstra recently wrote: "In particular we're very much all 'confused' about the various notions of transitivity". I am confused too, so - please use some more simple way to explain your words. Sorry, but we need a common ground first.
- Leonid. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
