> 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. I prefer _nocache_strict(), if it's not too long, since it avoids any confusion. If other arches actually implement it with WT semantics, we might become the one to change it, instead of the caller. Thanks, -Toshi
