> From: Jan Beulich [mailto:jbeul...@suse.com] > Sent: Tuesday, July 21, 2015 3:17 PM > >>> On 21.07.15 at 09:05, <kevin.t...@intel.com> wrote: > >> From: Jan Beulich [mailto:jbeul...@suse.com] > >> Sent: Tuesday, July 21, 2015 2:57 PM > >> >>> On 21.07.15 at 02:57, <kevin.t...@intel.com> wrote: > >> >> From: Andrew Cooper [mailto:am...@hermes.cam.ac.uk] On Behalf Of Andrew > >> > Cooper > >> >> Sent: Monday, July 20, 2015 4:21 PM > >> > This is the part which I don't quite understand. WC is essentially an UC > >> > attribute with write buffer to accelerate the write efficiency. There > >> > should be no correctness problem to use either WC or UC if i915 driver > >> > wants WC. > >> > >> "Should" is too weak a term here: Using WC on the wrong piece of > >> memory or without the necessary fencing can imo very well cause > >> correctness problems (which would be hidden by WC -> UC > >> conversion behind the driver's back). > >> > > > > My point is about when i915 wants WC, then either UC (I suppose is > > the case before that Linux commit) and WC (by that commit) has > > no correctness problem. UC is more strict than WC. It's just performance > > difference. It's not about using WC in wrong place when it's not desired. > > In this you assume there are no misguided attempts to request > WC in the driver, which would have gone unnoticed as long as WC > didn't become the effective attribute. And "misguided" here is > meant to include cases where hardware errata may need taking > care of. >
I don't understand this point. If it's misguided attempts it'd be same on bare metal. Thanks Kevin _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
