On 01/10/2019 13:22, Chris Wilson wrote:
Quoting Tvrtko Ursulin (2019-10-01 13:16:19)
On 01/10/2019 10:51, Chris Wilson wrote:
+
+ /*
+ * Setup the pair of contexts such that if we
+ * lite-restore using the RING_TAIL from ce[1] it
+ * will execute garbage from ce[0]->ring.
+ */
+ memset(ce[n]->ring->vaddr,
+ POISON_INUSE,
+ ce[n]->ring->vma->size);
+ }
+ intel_ring_reset(ce[1]->ring, ce[1]->ring->vma->size / 2);
+ __execlists_update_reg_state(ce[1], engine);
+
+ rq[0] = igt_spinner_create_request(&spin, ce[0], MI_ARB_CHECK);
+ if (IS_ERR(rq[0])) {
+ err = PTR_ERR(rq[0]);
+ goto err_ce;
+ }
+
+ GEM_BUG_ON(rq[0]->tail > ce[1]->ring->emit);
+ i915_request_get(rq[0]);
+ i915_request_add(rq[0]);
+
+ if (!igt_wait_for_spinner(&spin, rq[0])) {
+ i915_request_put(rq[0]);
+ goto err_ce;
+ }
+
+ rq[1] = i915_request_create(ce[1]);
+ if (IS_ERR(rq[1])) {
+ err = PTR_ERR(rq[1]);
+ i915_request_put(rq[0]);
+ goto err_ce;
+ }
+ GEM_BUG_ON(rq[1]->tail <= rq[0]->tail);
+
+ /* Ensure we do a completion switch from ce[0] to ce[1] */
+ i915_request_await_dma_fence(rq[1], &rq[0]->fence);
What do you mean by completion switch? You are setting up a dependency
so rq[1] (and rq[2]) won't be put into the elsp until spinner is ended
so it may not even be a context switch. Wouldn't you actually need the
opposite? I was expecting you would let the spinner run, make sure rq[1]
is in elsp and then count on time slicing to trigger a context switch.
The test I had in mind was to have
ELSP[0] = ce[0]
ELSP[1] = ce[1]
and so chose to prevent any timeslicing reordering that. Same engine, so
it will add a wait-on-submit-fence (i.e. a no-op) but would install the
dependency link to prevent any reordering.
Ah my bad, did not think about the same engine optimisation. Expand the
comment? :)
A second test to have the spinner running then using priority to preempt
it, seems like a good addition.
Priority it more controllable than timeslicing, true.
Regards,
Tvrtko
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