On Sat, May 6, 2017 at 2:46 AM, Ingo Molnar <mingo@xxxxxxxxxx> wrote: > > * Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > >> 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. > > Perhaps a _nocache_flush() postfix, to signal both that it's non-temporal and that > no cache line is left around afterwards (dirty or clean)? Yes, I think "flush" belongs in the name, and to make it easily grep-able separate from _nocache we can call it _flushcache? An efficient implementation will use _nocache / non-temporal stores internally, but external consumers just care about the state of the cache after the call.
