[Mesa-stable] [Mesa-dev] [PATCH 1/3] i965: Fix shared local memory size for Gen9+.

[Kenneth Graunke]

On Thursday, June 9, 2016 10:00:40 AM PDT Ilia Mirkin wrote:
> On Jun 9, 2016 4:10 AM, "Kenneth Graunke" <kenneth at whitecape.org> wrote:
> >
> > Skylake changes the representation of shared local memory size:
> >
> >  Size   | 0 kB | 1 kB | 2 kB | 4 kB | 8 kB | 16 kB | 32 kB | 64 kB |
> >  -------------------------------------------------------------------
> >  Gen7-8 |    0 | none | none |    1 |    2 |     3 |     4 |     5 |
> >  -------------------------------------------------------------------
> >  Gen9+  |    0 |    1 |    2 |    3 |    4 |     5 |     6 |     7 |
> >
> > The old formula would substantially underallocate the amount of space.
> > This fixes GPU hangs on Skylake when running with full thread counts.
> >
> > Cc: "12.0" <mesa-stable at lists.freedesktop.org>
> > Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
> > ---
> >  src/mesa/drivers/dri/i965/gen7_cs_state.c | 15 ++++++++++-----
> >  1 file changed, 10 insertions(+), 5 deletions(-)
> >
> > diff --git a/src/mesa/drivers/dri/i965/gen7_cs_state.c
> b/src/mesa/drivers/dri/i965/gen7_cs_state.c
> > index 750aa2c..aff1f4e 100644
> > --- a/src/mesa/drivers/dri/i965/gen7_cs_state.c
> > +++ b/src/mesa/drivers/dri/i965/gen7_cs_state.c
> > @@ -150,11 +150,16 @@ brw_upload_cs_state(struct brw_context *brw)
> >     assert(prog_data->total_shared <= 64 * 1024);
> >     uint32_t slm_size = 0;
> >     if (prog_data->total_shared > 0) {
> > -      /* slm_size is in 4k increments, but must be a power of 2. */
> > -      slm_size = 4 * 1024;
> > -      while (slm_size < prog_data->total_shared)
> > -         slm_size <<= 1;
> > -      slm_size /= 4 * 1024;
> > +      /* Shared Local Memory Size is specified as powers of two. */
> > +      slm_size = util_next_power_of_two(prog_data->total_shared);
> > +
> > +      if (brw->gen >= 9) {
> > +         /* Use a minimum of 1kB; turn an exponent of 10 (1024 kB) into
> 1. */
> > +         slm_size = ffs(MAX2(slm_size, 1024)) - 10;
> > +      } else {
> > +         /* Use a minimum of 4kB; convert to the pre-Gen9
> representation. */
> > +         slm_size = MAX2(slm_size, 4096) / 4096;
> 
> According to your chart, 16k should end up with 3, but this logic will
> produce 4. The old comment said it was in increments of 4k, so I'm guessing
> just the chart needs to be adjusted.

Yikes, sorry!  A wrong chart is better than no chart at all.  I meant:

  Size   | 0 kB | 1 kB | 2 kB | 4 kB | 8 kB | 16 kB | 32 kB | 64 kB |
  -------------------------------------------------------------------
  Gen7-8 |    0 | none | none |    1 |    2 |     4 |     8 |    16 |
  -------------------------------------------------------------------
  Gen9+  |    0 |    1 |    2 |    3 |    4 |     5 |     6 |     7 |

I should probably move this code to a helper function and put the
(correct) table in a comment...
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