[Intel-gfx] [PATCH] drm/i915/execlists: Drop preemption arbitrations points along the ring

[Chris Wilson]

Limit the arbitration (where preemption may occur) to inside the batch,
and prevent it from happening on the pipecontrols/flushes we use to
write the breadcrumb seqno. Once the user batch is complete, we have
nothing left to do but serialise and emit the breadcrumb; switching
contexts at this point is futile so don't.

Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
Cc: Michał Winiarski <michal.winiar...@intel.com>
Cc: Michel Thierry <michel.thie...@intel.com>
Cc: Joonas Lahtinen <joonas.lahti...@linux.intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursu...@intel.com>
---

Michał and Michel,
  please take a look and see if you can think of any objections.
-Chris

---
 drivers/gpu/drm/i915/intel_lrc.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 3d747d1c3d4d..9f3cce022b2d 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1933,7 +1933,7 @@ static int gen8_emit_bb_start(struct i915_request *rq,
                rq->ctx->ppgtt->pd_dirty_rings &= 
~intel_engine_flag(rq->engine);
        }
 
-       cs = intel_ring_begin(rq, 4);
+       cs = intel_ring_begin(rq, 6);
        if (IS_ERR(cs))
                return PTR_ERR(cs);
 
@@ -1962,6 +1962,9 @@ static int gen8_emit_bb_start(struct i915_request *rq,
                (flags & I915_DISPATCH_RS ? MI_BATCH_RESOURCE_STREAMER : 0);
        *cs++ = lower_32_bits(offset);
        *cs++ = upper_32_bits(offset);
+
+       *cs++ = MI_ARB_ON_OFF | MI_ARB_DISABLE;
+       *cs++ = MI_NOOP;
        intel_ring_advance(rq, cs);
 
        return 0;
@@ -2104,7 +2107,7 @@ static void gen8_emit_breadcrumb(struct i915_request 
*request, u32 *cs)
        cs = gen8_emit_ggtt_write(cs, request->global_seqno,
                                  intel_hws_seqno_address(request->engine));
        *cs++ = MI_USER_INTERRUPT;
-       *cs++ = MI_NOOP;
+       *cs++ = MI_ARB_ON_OFF | MI_ARB_ENABLE;
        request->tail = intel_ring_offset(request, cs);
        assert_ring_tail_valid(request->ring, request->tail);
 
@@ -2120,7 +2123,7 @@ static void gen8_emit_breadcrumb_rcs(struct i915_request 
*request, u32 *cs)
        cs = gen8_emit_ggtt_write_rcs(cs, request->global_seqno,
                                      intel_hws_seqno_address(request->engine));
        *cs++ = MI_USER_INTERRUPT;
-       *cs++ = MI_NOOP;
+       *cs++ = MI_ARB_ON_OFF | MI_ARB_ENABLE;
        request->tail = intel_ring_offset(request, cs);
        assert_ring_tail_valid(request->ring, request->tail);
 
-- 
2.17.0

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