[Mesa-dev] [PATCH] i965/skl: Use larger URB size where available.

[Ben Widawsky]

On Fri, Sep 11, 2015 at 12:12:15PM -0700, Jordan Justen wrote:
> On 2015-09-10 16:59:12, Ben Widawsky wrote:
> > All SKL SKUs except the lowest one which has half the L3 size actually have 384K
> 
> These commit message lines seem to wrap a bit long. This first line is
> 80 characters.
> 
> > of URB per slice.
> > 
> > For once, I can explain how this mistake was made and how it was missed in
> > review...  Historically when we enable a platform and put the production sizes,
> > you can simply look at the "smallest" SKU and see what its URB size is (and we
> > assumed it was the 1 slice variant). Since on newer platforms the URB sizes are
> > scaled automatically by HW, this was sufficient. On SKL, this is a bit different
> > as the lowest SKU actually has half of the L3 fused off. GT2 is the 1 slice (not
> > GT1) variant and it has 384K.
> > 
> > There are no Jenkins tests fixed (or regressions) and we don't expect any fixes
> > here because you can always run with less URB size - this potentially improves
> > performance.
> 
> It would be nice if we were able to find a benchmark that improves
> from this change. If we can't then maybe we should just remove this
> paragraph. It seems like the right change regardless.
> 
> Reviewed-by: Jordan Justen <jordan.l.justen at intel.com>

I think what I'd like to do is run the perf data to make sure there are at least
no regressions since I am proposing it for stable... Maybe if I don't get around
to that before the next stable release, we'll bail on it for 10.6

> 
> > Thanks to Sarah for bringing this to my attention.
> 
> Reported-by?
> 
> > Cc: "10.6 11.0" <mesa-stable at lists.freedesktop.org>
> > Cc: Neil Roberts <neil at linux.intel.com>
> > Cc: Sarah Sharp <sarah.a.sharp at intel.com>
> > Cc: Jordan Justen <jordan.l.justen at intel.com>
> > Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
> > ---
> >  src/mesa/drivers/dri/i965/brw_device_info.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/src/mesa/drivers/dri/i965/brw_device_info.c b/src/mesa/drivers/dri/i965/brw_device_info.c
> > index 7ad3a2f..a6a3bb6 100644
> > --- a/src/mesa/drivers/dri/i965/brw_device_info.c
> > +++ b/src/mesa/drivers/dri/i965/brw_device_info.c
> > @@ -314,7 +314,7 @@ static const struct brw_device_info brw_device_info_chv = {
> >     .max_wm_threads = 64 * 6,                        \
> >     .max_cs_threads = 56,                            \
> >     .urb = {                                         \
> > -      .size = 192,                                  \
> > +      .size = 384,                                  \
> >        .min_vs_entries = 64,                         \
> >        .max_vs_entries = 1856,                       \
> >        .max_hs_entries = 672,                        \
> > @@ -324,6 +324,7 @@ static const struct brw_device_info brw_device_info_chv = {
> >  
> >  static const struct brw_device_info brw_device_info_skl_gt1 = {
> >     GEN9_FEATURES, .gt = 1,
> > +   .urb.size = 192,
> >  };
> >  
> >  static const struct brw_device_info brw_device_info_skl_gt2 = {
> > -- 
> > 2.5.1
> >