> * Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > > > 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. > > _flushcache() works for me too. > Works for me too. Thanks, -Toshi
