Quoting Mika Kuoppala (2020-06-13 09:44:39) > Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes: > > > Quoting Mika Kuoppala (2020-06-12 23:05:18) > >> Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes: > >> > >> > gen3 does not fully flush MI stores to memory on MI_FLUSH, such that a > >> > subsequent read from e.g. the sampler can bypass the store and read the > >> > stale value from memory. This is a serious issue when we are using MI > >> > stores to rewrite the batches for relocation, as it means that the batch > >> > is reading from random user/kernel memory. While it is particularly > >> > sensitive [and detectable] for relocations, reading stale data at any > >> > time is a worry. > >> > > >> > Having started with a small number of delaying stores and doubling until > >> > no more incoherency was seen over a few hours (with and without > >> > background memory pressure), 32 was the magic number. > >> > > >> > v2: Follow more closer with the gen5 w/a and include some > >> > post-invalidate flushes as well. > >> > > >> > Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2018 > >> > References: a889580c087a ("drm/i915: Flush GPU relocs harder for gen3") > >> > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > >> > Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx> > >> > Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx> > >> > --- > >> > drivers/gpu/drm/i915/gt/gen2_engine_cs.c | 61 ++++++++++-------------- > >> > 1 file changed, 25 insertions(+), 36 deletions(-) > >> > > >> > diff --git a/drivers/gpu/drm/i915/gt/gen2_engine_cs.c b/drivers/gpu/drm/i915/gt/gen2_engine_cs.c > >> > index 3fb0dc1fb910..5400d657f334 100644 > >> > --- a/drivers/gpu/drm/i915/gt/gen2_engine_cs.c > >> > +++ b/drivers/gpu/drm/i915/gt/gen2_engine_cs.c > >> > @@ -13,28 +13,25 @@ > >> > > >> > int gen2_emit_flush(struct i915_request *rq, u32 mode) > >> > { > >> > - unsigned int num_store_dw; > >> > + unsigned int num_store_dw = 12; > >> > u32 cmd, *cs; > >> > > >> > cmd = MI_FLUSH; > >> > - num_store_dw = 0; > >> > if (mode & EMIT_INVALIDATE) > >> > cmd |= MI_READ_FLUSH; > >> > - if (mode & EMIT_FLUSH) > >> > - num_store_dw = 4; > >> > > >> > - cs = intel_ring_begin(rq, 2 + 3 * num_store_dw); > >> > + cs = intel_ring_begin(rq, 2 + 4 * num_store_dw); > >> > if (IS_ERR(cs)) > >> > return PTR_ERR(cs); > >> > > >> > *cs++ = cmd; > >> > while (num_store_dw--) { > >> > - *cs++ = MI_STORE_DWORD_IMM | MI_MEM_VIRTUAL; > >> > - *cs++ = intel_gt_scratch_offset(rq->engine->gt, > >> > - INTEL_GT_SCRATCH_FIELD_DEFAULT); > >> > - *cs++ = 0; > >> > + *cs++ = MI_STORE_DWORD_INDEX; > >> > + *cs++ = I915_GEM_HWS_SCRATCH * sizeof(u32); > >> > + *cs++ = rq->fence.seqno - 1; > >> > + *cs++ = MI_FLUSH | MI_NO_WRITE_FLUSH; > >> > } > >> > - *cs++ = MI_FLUSH | MI_NO_WRITE_FLUSH; > >> > + *cs++ = cmd; > >> > > >> > intel_ring_advance(rq, cs); > >> > > >> > @@ -142,38 +139,21 @@ int gen4_emit_flush_vcs(struct i915_request *rq, u32 mode) > >> > return 0; > >> > } > >> > > >> > -u32 *gen3_emit_breadcrumb(struct i915_request *rq, u32 *cs) > >> > +static u32 *__gen2_emit_breadcrumb(struct i915_request *rq, u32 *cs, > >> > + int flush, int post) > >> > { > >> > 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; > >> > > >> > - *cs++ = MI_STORE_DWORD_INDEX; > >> > - *cs++ = I915_GEM_HWS_SEQNO_ADDR; > >> > - *cs++ = rq->fence.seqno; > >> > - > >> > - *cs++ = MI_USER_INTERRUPT; > >> > >> How can you throw the interrupt part out? > > > > Diff being confusing. gen3_emit_breadcrumb and gen5_emit_breadcrumb > > merged together. > > Reviewed-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx> It failed eventually, so unfortunately it's still just paper. However increasing the MTBF by a few orders of magnitude should be enough to stop CI complaining on every idle run. -Chris _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
