On 27/07/15 16:57, O'Rourke, Tom wrote:
On Thu, Jul 09, 2015 at 07:29:12PM +0100, Dave Gordon wrote:
From: Alex Dai <yu.dai@xxxxxxxxx>
GuC-based submission is mostly the same as execlist mode, up to
intel_logical_ring_advance_and_submit(), where the context being
dispatched would be added to the execlist queue; at this point
we submit the context to the GuC backend instead.
There are, however, a few other changes also required, notably:
1. Contexts must be pinned at GGTT addresses accessible by the GuC
i.e. NOT in the range [0..WOPCM_SIZE), so we have to add the
PIN_OFFSET_BIAS flag to the relevant GGTT-pinning calls.
2. The GuC's TLB must be invalidated after a context is pinned at
a new GGTT address.
[snip]
static int gen8_init_rcs_context(struct drm_i915_gem_request *req)
{
+ struct drm_i915_private *dev_priv = req->i915;
int ret;
+ /* Invalidate GuC TLB. */
+ if (i915.enable_guc_submission)
+ I915_WRITE(GEN8_GTCR, GEN8_GTCR_INVALIDATE);
+
>
[TOR:] This invalidation is in the init_context for render
ring but not the other rings. Is this needed for other
rings? Or, should this invalidation happen at a different
level? It seems this may depend on the on render ring being
initialized first.
Thanks,
Tom
Hi Tom,
it looks like this is redundant here in the case where its called from
the non-default-context case of intel_lr_context_deferred_create(); but
when called from i915_gem_init_hw() [via i915_gem_context_enable()] it
wouldn't be, because the GuC TLB wouldn't have been flushed since the
default context was pinned [which is in a completely different path
through intel_lr_context_deferred_create()!].
However, if we add a TLB flush just after that point, we can remove this
one here, with several advantages:
* firstly, that path is taken just once, rather than every time a new
render context is created, and
* secondly, each flush can be specifically associated with a pin-to-gtt
call that includes the (PIN_OFFSET_BIAS | GUC_WOPCM_SIZE_VALUE) flags,
showing that the pinned object is of interest to the GuC.
I'll also move the existing TLB flushes in guc_submission.c and
guc_loader.c so that they're also just after the relevant 'pin' calls.
Thanks,
.Dave.
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