On Fri, May 5, 2017 at 3:44 PM, Kani, Toshimitsu <toshi.kani@xxxxxxx> wrote: > On Fri, 2017-05-05 at 15:25 -0700, Dan Williams wrote: >> On Fri, May 5, 2017 at 1:39 PM, Kani, Toshimitsu <toshi.kani@xxxxxxx> >> wrote: > : >> > > --- >> > > Changes since the initial RFC: >> > > * s/writethru/wt/ since we already have ioremap_wt(), >> > > set_memory_wt(), etc. (Ingo) >> > >> > Sorry I should have said earlier, but I think the term "wt" is >> > misleading. Non-temporal stores used in memcpy_wt() provide WC >> > semantics, not WT semantics. >> >> The non-temporal stores do, but memcpy_wt() is using a combination of >> non-temporal stores and explicit cache flushing. >> >> > How about using "nocache" as it's been >> > used in __copy_user_nocache()? >> >> The difference in my mind is that the "_nocache" suffix indicates >> opportunistic / optional cache pollution avoidance whereas "_wt" >> strictly arranges for caches not to contain dirty data upon >> completion of the routine. For example, non-temporal stores on older >> x86 cpus could potentially leave dirty data in the cache, so >> memcpy_wt on those cpus would need to use explicit cache flushing. > > I see. I agree that its behavior is different from the existing one > with "_nocache". That said, I think "wt" or "write-through" generally > means that writes allocate cachelines and keep them clean by writing to > memory. So, subsequent reads to the destination will hit the > cachelines. This is not the case with this interface. True... maybe _nocache_strict()? Or, leave it _wt() until someone comes along and is surprised that the cache is not warm for reads after memcpy_wt(), at which point we can ask "why not just use plain memcpy then?", or set the page-attributes to WT.
