[4/7] drm/i915: Cache LRC state page in the context

Commit Message

Tvrtko Ursulin Jan. 11, 2016, 2:08 p.m. UTC

From: Tvrtko Ursulin <[e-mail]>

LRC lifetime is well defined so we can cache the page pointing
to the object backing store in the context in order to avoid
walking over the object SG page list from the interrupt context
without the big lock held.

Signed-off-by: Tvrtko Ursulin <[e-mail]>
---
 drivers/gpu/drm/i915/i915_drv.h  |  1 +
 drivers/gpu/drm/i915/intel_lrc.c | 17 +++++++++++------
 2 files changed, 12 insertions(+), 6 deletions(-)

Comments

Chris Wilson Jan. 11, 2016, 2:29 p.m. UTC | #1

On Mon, Jan 11, 2016 at 02:08:38PM +0000, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <[e-mail]>
> 
> LRC lifetime is well defined so we can cache the page pointing
> to the object backing store in the context in order to avoid
> walking over the object SG page list from the interrupt context
> without the big lock held.

You can keep kmap around for the pinned lifetime of the context.
-Chris

Tvrtko Ursulin Jan. 11, 2016, 3:07 p.m. UTC | #2

On 11/01/16 14:29, Chris Wilson wrote:
> On Mon, Jan 11, 2016 at 02:08:38PM +0000, Tvrtko Ursulin wrote:
>> From: Tvrtko Ursulin <[e-mail]>
>>
>> LRC lifetime is well defined so we can cache the page pointing
>> to the object backing store in the context in order to avoid
>> walking over the object SG page list from the interrupt context
>> without the big lock held.
>
> You can keep kmap around for the pinned lifetime of the context.

Baby steps. :)

Regards,

Tvrtko

Patch

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 4b0932634cc9..377cdcb10ad5 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -885,6 +885,7 @@  struct intel_context {
 		int pin_count;
 		u32 lrc_offset;
 		u64 lrc_desc;
+		struct page *lrc_state_page;
 	} engine[I915_NUM_RINGS];
 
 	struct list_head link;
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 321674d5e1f9..02ef9413700d 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -338,14 +338,10 @@  static int execlists_update_context(struct drm_i915_gem_request *rq)
 {
 	struct intel_engine_cs *ring = rq->ring;
 	struct i915_hw_ppgtt *ppgtt = rq->ctx->ppgtt;
-	struct drm_i915_gem_object *ctx_obj = rq->ctx->engine[ring->id].state;
-	struct page *page;
 	uint32_t *reg_state;
 
-	BUG_ON(!ctx_obj);
-
-	page = i915_gem_object_get_dirty_page(ctx_obj, LRC_STATE_PN);
-	reg_state = kmap_atomic(page);
+	BUG_ON(!rq->ctx->engine[ring->id].lrc_state_page);
+	reg_state = kmap_atomic(rq->ctx->engine[ring->id].lrc_state_page);
 
 	reg_state[CTX_RING_TAIL+1] = rq->tail;
 	reg_state[CTX_RING_BUFFER_START+1] = rq->ringbuf->gtt_offset;
@@ -1015,6 +1011,7 @@  static int intel_lr_context_do_pin(struct intel_engine_cs *ring,
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct drm_i915_gem_object *ctx_obj = ctx->engine[ring->id].state;
 	struct intel_ringbuffer *ringbuf = ctx->engine[ring->id].ringbuf;
+	struct page *lrc_state_page;
 	int ret;
 
 	WARN_ON(!mutex_is_locked(&ring->dev->struct_mutex));
@@ -1024,6 +1021,12 @@  static int intel_lr_context_do_pin(struct intel_engine_cs *ring,
 	if (ret)
 		return ret;
 
+	lrc_state_page = i915_gem_object_get_dirty_page(ctx_obj, LRC_STATE_PN);
+	if (WARN_ON(!lrc_state_page)) {
+		ret = -ENODEV;
+		goto unpin_ctx_obj;
+	}
+
 	ret = intel_pin_and_map_ringbuffer_obj(ring->dev, ringbuf);
 	if (ret)
 		goto unpin_ctx_obj;
@@ -1033,6 +1036,7 @@  static int intel_lr_context_do_pin(struct intel_engine_cs *ring,
 	ctx->engine[ring->id].lrc_desc = ring->ctx_desc_template |
 					 ctx->engine[ring->id].lrc_offset |
 					 ((u64)intel_execlists_ctx_id(ctx, ring) << GEN8_CTX_ID_SHIFT);
+	ctx->engine[ring->id].lrc_state_page = lrc_state_page;
 	ctx_obj->dirty = true;
 
 	/* Invalidate GuC TLB. */
@@ -1077,6 +1081,7 @@  void intel_lr_context_unpin(struct drm_i915_gem_request *rq)
 			i915_gem_object_ggtt_unpin(ctx_obj);
 			rq->ctx->engine[ring->id].lrc_offset = 0;
 			rq->ctx->engine[ring->id].lrc_desc = 0;
+			rq->ctx->engine[ring->id].lrc_state_page = NULL;
 		}
 	}
 }