[Intel-gfx] [PATCH 1/2] drm/i915/sseu: Don't overallocate subslice storage

[Matt Roper]

On Fri, Mar 11, 2022 at 11:01:01PM +0200, Ville Syrjälä wrote:
> On Fri, Mar 11, 2022 at 12:52:33PM -0800, Lucas De Marchi wrote:
> > On Fri, Mar 11, 2022 at 12:43:40PM -0800, Matt Roper wrote:
> > >On Fri, Mar 11, 2022 at 12:38:17PM -0800, Matt Roper wrote:
> > >> On Fri, Mar 11, 2022 at 11:00:09AM -0800, Lucas De Marchi wrote:
> > >> > On Thu, Mar 10, 2022 at 10:15:42PM -0800, Matt Roper wrote:
> > >> > > Xe_HP removed "slice" as a first-class unit in the hardware design.
> > >> > > Instead we now have a single pool of subslices (which are now referred
> > >> > > to as "DSS") that different hardware units have different ways of
> > >> > > grouping ("compute slices," "geometry slices," etc.).  For the purposes
> > >> > > of topology representation, we treat Xe_HP-based platforms as having a
> > >> > > single slice that contains all of the platform's DSS.  There's no need
> > >> > > to allocate storage space for (max legacy slices * max dss); let's
> > >> > > update some of our macros to minimize the storage requirement for sseu
> > >> > > topology.  We'll also document some of the constants to make it a little
> > >> > > bit more clear what they represent.
> > >> > >
> > >> > > Signed-off-by: Matt Roper <matthew.d.roper at intel.com>
> > >> > > ---
> > >> > > drivers/gpu/drm/i915/gt/intel_engine_types.h |  2 +-
> > >> > > drivers/gpu/drm/i915/gt/intel_sseu.h         | 47 +++++++++++++++-----
> > >> > > 2 files changed, 36 insertions(+), 13 deletions(-)
> > >> > >
> > >> > > diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h
> > >> > > index 4fbf45a74ec0..f9e246004bc0 100644
> > >> > > --- a/drivers/gpu/drm/i915/gt/intel_engine_types.h
> > >> > > +++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h
> > >> > > @@ -645,7 +645,7 @@ intel_engine_has_relative_mmio(const struct intel_engine_cs * const engine)
> > >> > >
> > >> > > #define for_each_instdone_gslice_dss_xehp(dev_priv_, sseu_, iter_, gslice_, dss_) \
> > >> > > 	for ((iter_) = 0, (gslice_) = 0, (dss_) = 0; \
> > >> > > -	     (iter_) < GEN_MAX_SUBSLICES; \
> > >> > > +	     (iter_) < GEN_SS_MASK_SIZE; \
> > >> > > 	     (iter_)++, (gslice_) = (iter_) / GEN_DSS_PER_GSLICE, \
> > >> > > 	     (dss_) = (iter_) % GEN_DSS_PER_GSLICE) \
> > >> > > 		for_each_if(intel_sseu_has_subslice((sseu_), 0, (iter_)))
> > >> > > diff --git a/drivers/gpu/drm/i915/gt/intel_sseu.h b/drivers/gpu/drm/i915/gt/intel_sseu.h
> > >> > > index 8a79cd8eaab4..4f59eadbb61a 100644
> > >> > > --- a/drivers/gpu/drm/i915/gt/intel_sseu.h
> > >> > > +++ b/drivers/gpu/drm/i915/gt/intel_sseu.h
> > >> > > @@ -15,26 +15,49 @@ struct drm_i915_private;
> > >> > > struct intel_gt;
> > >> > > struct drm_printer;
> > >> > >
> > >> > > -#define GEN_MAX_SLICES		(3) /* SKL upper bound */
> > >> > > -#define GEN_MAX_SUBSLICES	(32) /* XEHPSDV upper bound */
> > >> > > -#define GEN_SSEU_STRIDE(max_entries) DIV_ROUND_UP(max_entries, BITS_PER_BYTE)
> > >> > > -#define GEN_MAX_SUBSLICE_STRIDE GEN_SSEU_STRIDE(GEN_MAX_SUBSLICES)
> > >> > > -#define GEN_MAX_EUS		(16) /* TGL upper bound */
> > >> > > -#define GEN_MAX_EU_STRIDE GEN_SSEU_STRIDE(GEN_MAX_EUS)
> > >> > > +/*
> > >> > > + * Maximum number of legacy slices.  Legacy slices no longer exist starting on
> > >> > > + * Xe_HP ("gslices," "cslices," etc. on Xe_HP and beyond are a different
> > >> > > + * concept and are not expressed through fusing).
> > >> > > + */
> > >> > > +#define GEN_MAX_LEGACY_SLICES		3
> > >> > > +
> > >> > > +/*
> > >> > > + * Maximum number of subslices that can exist within a legacy slice.  This is
> > >> > > + * only relevant to pre-Xe_HP platforms (Xe_HP and beyond use the GEN_MAX_DSS
> > >> > > + * value below).
> > >> > > + */
> > >> > > +#define GEN_MAX_LEGACY_SUBSLICES	6
> > >> >
> > >> > instead of calling the old legacy, maybe just add the XEHP_ prefix to
> > >> > the new ones?
> > >>
> > >> Maybe a "HSW_" prefix on the old ones would be better?  People still use
> > >> the termm 'subslice' in casual discussion when talking about DSS, so I
> > >> want to somehow distinguish that what we're talking about here is a
> > >> different, older design than we have on modern platforms.
> > >
> > >Hmm, or maybe just "GEN_MAX_SUBSLICES_PER_LEGACY_SLICE" to tie it into
> > >the slice definition above?
> > 
> > I'm not too fond of calling it "legacy" when everywhere else in the driver
> > we just use the platform as prefix/suffix. Some may see legacy as
> > < ver 12, others as 12.50, etc.
> 
> Everything will become legacy at some point. This kind of naming
> scheme falls apart when the next shiny new thing comes around
> and we end up with multiple different leagacies. Are we going
> to have ANCIENT_LEGACY, RECENT_LEGACY, NOT_YET_LEGACY etc?

Well that's kind of the point --- there is no shiny new thing and never
will be.  "slice" is gone for good and the places we use the term are
_not_ the same thing as similar-sounding terms like gslice, cslice,
mslice, etc.

But I'll go ahead and switch it to "HSW_" and hope people figure out
that it stops being a meaningful concept Xe_HP.


Matt

> 
> -- 
> Ville Syrjälä
> Intel

-- 
Matt Roper
Graphics Software Engineer
VTT-OSGC Platform Enablement
Intel Corporation
(916) 356-2795