[Intel-gfx] [PATCH] drm/i915/gt: Invalidate as we write the gen7 breadcrumb

[Chris Wilson]

Quoting Mika Kuoppala (2019-11-13 15:59:53)
> Chris Wilson <chris at chris-wilson.co.uk> writes:
> 
> > Still the saga of the hsw live_blt incoherency continues. While it did
> > seem that the invalidate before the breadcrumb had improved the mtbf,
> > nevertheless live_blt still failed. Mika's next idea was to pull the
> > invalidate-stall into the breadcrumb write itself.
> >
> > References: 860afa086841 ("drm/i915/gt: Flush gen7 even harder")
> > References: https://bugs.freedesktop.org/show_bug.cgi?id=112147
> > Testcase: igt/i915_selftest/live_blt
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/gt/intel_ring_submission.c | 9 +++------
> >  1 file changed, 3 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gt/intel_ring_submission.c b/drivers/gpu/drm/i915/gt/intel_ring_submission.c
> > index e8bee44add34..f25ceccb335e 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_ring_submission.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_ring_submission.c
> > @@ -454,12 +454,8 @@ static u32 *gen7_xcs_emit_breadcrumb(struct i915_request *rq, u32 *cs)
> >       GEM_BUG_ON(i915_request_active_timeline(rq)->hwsp_ggtt != rq->engine->status_page.vma);
> >       GEM_BUG_ON(offset_in_page(i915_request_active_timeline(rq)->hwsp_offset) != I915_GEM_HWS_SEQNO_ADDR);
> >  
> > -     *cs++ = (MI_FLUSH_DW | MI_INVALIDATE_TLB |
> > -              MI_FLUSH_DW_STORE_INDEX | MI_FLUSH_DW_OP_STOREDW);
> > -     *cs++ = I915_GEM_HWS_SCRATCH_ADDR | MI_FLUSH_DW_USE_GTT;
> > -     *cs++ = 0;
> > -
> > -     *cs++ = MI_FLUSH_DW | MI_FLUSH_DW_OP_STOREDW | MI_FLUSH_DW_STORE_INDEX;
> > +     *cs++ = MI_FLUSH_DW | MI_INVALIDATE_TLB |
> > +             MI_FLUSH_DW_OP_STOREDW | MI_FLUSH_DW_STORE_INDEX;
> >       *cs++ = I915_GEM_HWS_SEQNO_ADDR | MI_FLUSH_DW_USE_GTT;
> >       *cs++ = rq->fence.seqno;
> 
> In both would have been the shotgun approach. You favour sniper.

At the end of the day, we stop when live_blt stops failing -- and we
hope that it's in the simplest form when we forget about it :)
-Chris