[Intel-gfx] [PATCH 2/4] drm/i915/gt: Check for arbitration after writing start seqno
tvrtko.ursulin at linux.intel.com
Mon Jan 11 16:03:48 UTC 2021
On 11/01/2021 10:57, Chris Wilson wrote:
> On the off chance that we need to arbitrate before launching the
> payload, perform the check after we signal the request is ready to
> start. Assuming instantaneous processing of the CS event, the request
> will then be treated as having started when we make the decisions as to
> how to process that CS event.
What is the wider context with this change?
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> drivers/gpu/drm/i915/gt/gen8_engine_cs.c | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)
> diff --git a/drivers/gpu/drm/i915/gt/gen8_engine_cs.c b/drivers/gpu/drm/i915/gt/gen8_engine_cs.c
> index 2e36e0a9d8a6..9a182652a35e 100644
> --- a/drivers/gpu/drm/i915/gt/gen8_engine_cs.c
> +++ b/drivers/gpu/drm/i915/gt/gen8_engine_cs.c
> @@ -361,19 +361,19 @@ int gen8_emit_init_breadcrumb(struct i915_request *rq)
> if (IS_ERR(cs))
> return PTR_ERR(cs);
> + *cs++ = MI_STORE_DWORD_IMM_GEN4 | MI_USE_GGTT;
> + *cs++ = hwsp_offset(rq);
> + *cs++ = 0;
> + *cs++ = rq->fence.seqno - 1;
Strictly this movement even makes the existing comment (below) more correct.
> * Check if we have been preempted before we even get started.
> * After this point i915_request_started() reports true, even if
> * we get preempted and so are no longer running.
> - *cs++ = MI_ARB_CHECK;
> *cs++ = MI_NOOP;
> - *cs++ = MI_STORE_DWORD_IMM_GEN4 | MI_USE_GGTT;
> - *cs++ = hwsp_offset(rq);
> - *cs++ = 0;
> - *cs++ = rq->fence.seqno - 1;
> + *cs++ = MI_ARB_CHECK;
Special reason to have NOOP before MI_ARB_CHECK or would more common
NOOP padding at the end be suitable?
> intel_ring_advance(rq, cs);
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