[PATCH 15/25] drm/i915: Preallocate enough space for the average request

[Chris Wilson]

Rather than being interrupted when we run out of space halfway through
the request, and having to restart from the beginning (and returning to
userspace), flush a little more free space when we prepare the request.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_lrc.c        | 6 +++++-
 drivers/gpu/drm/i915/intel_ringbuffer.c | 7 ++++++-
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 1ecdebb88c1a..d2c41b85fad0 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -702,7 +702,11 @@ int intel_logical_ring_alloc_request_extras(struct drm_i915_gem_request *request
 
 	request->ringbuf = request->ctx->engine[request->engine->id].ringbuf;
 
-	ret = intel_ring_begin(request, 0);
+	/* Flush enough space to reduce the likelihood of waiting after
+	 * we start building the request - in which case we will just
+	 * have to repeat work.
+	 */
+	ret = intel_ring_begin(request, MIN_SPACE_FOR_ADD_REQUEST);
 	if (ret)
 		return ret;
 
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 68da54680efd..511a49fd9f02 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -2333,7 +2333,12 @@ int intel_engine_idle(struct intel_engine_cs *engine)
 int intel_ring_alloc_request_extras(struct drm_i915_gem_request *request)
 {
 	request->ringbuf = request->engine->buffer;
-	return intel_ring_begin(request, 0);
+
+	/* Flush enough space to reduce the likelihood of waiting after
+	 * we start building the request - in which case we will just
+	 * have to repeat work.
+	 */
+	return intel_ring_begin(request, MIN_SPACE_FOR_ADD_REQUEST);
 }
 
 static int wait_for_space(struct drm_i915_gem_request *req, int bytes)
-- 
2.8.1