[Mesa-dev] [PATCH 2/3] i965/gen7: Set MOCS L3 cacheability for IVB/BYT

[Chad Versace]

On 08/14/2013 12:50 AM, Ville Syrjälä wrote:
> On Wed, Aug 14, 2013 at 10:45:23AM +0300, Ville Syrjälä wrote:
>> On Tue, Aug 13, 2013 at 05:46:55PM -0700, Chad Versace wrote:
>>> On 08/13/2013 03:31 PM, Vedran Rodic wrote:
>>>> On Mon, Aug 12, 2013 at 3:07 PM,  <ville.syrjala at linux.intel.com> wrote:
>>>>> From: Ville Syrjälä <ville.syrjala at linux.intel.com>


>> For L3 cacheability, IVB won't consult the PTE for anything that has a
>> relevant MOCS field. So even if you make everything L3 cacheable through
>> the PTEs, MOCS will always override it. How do i know you ask? Well,
>> BSpec says so for one, and more importantly I verified this by running
>> some tests [...]


I suspected this. Thanks for sharing your experimental evidence.


>> For LLC cachebility the story will be different because there IVB MOCS
>> can only say "LLC cacheable" or "consult the PTE". So to make stuff
>> uncached in LLC on IVB, we'd need to issues the set_caching ioctl to
>> change the PTE to uncached, and after that we could use just the MOCS
>> to select the LLC caching policy. Since the set_caching ioctl only needs
>> to be issued once per object (or you could use the , there
>
> Sorry hit send by accident. Was going to say we could use the new
> create2 ioctl Chris has proposed that allows you to set the cache mode
> when creating the object. So there won't be a performance hit from
> extra ioctls getting issued all the time.


I would like such a cache-control ioctl, as long the ioctl can also
be used to change the object's cacheing policy in addition to
setting it at object creation. This would be
needed when an object's usage oscillates between texture surface
and render target.