[PATCH 15/26] 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        |  7 +++++++
 drivers/gpu/drm/i915/intel_ringbuffer.c | 16 +++++++++++++++-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 2c528657d6a2..7d5186e17317 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -700,6 +700,12 @@ int intel_logical_ring_alloc_request_extras(struct drm_i915_gem_request *request
 {
 	int ret;
 
+	/* 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.
+	 */
+	request->reserved_space += MIN_SPACE_FOR_ADD_REQUEST;
+
 	request->ringbuf = request->ctx->engine[request->engine->id].ringbuf;
 
 	if (i915.enable_guc_submission) {
@@ -725,6 +731,7 @@ int intel_logical_ring_alloc_request_extras(struct drm_i915_gem_request *request
 	if (ret)
 		return ret;
 
+	request->reserved_space -= MIN_SPACE_FOR_ADD_REQUEST;
 	return 0;
 }
 
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 68da54680efd..de36b8e27025 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -2332,8 +2332,22 @@ int intel_engine_idle(struct intel_engine_cs *engine)
 
 int intel_ring_alloc_request_extras(struct drm_i915_gem_request *request)
 {
+	int ret;
+
+	/* 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.
+	 */
+	request->reserved_space += MIN_SPACE_FOR_ADD_REQUEST;
+
 	request->ringbuf = request->engine->buffer;
-	return intel_ring_begin(request, 0);
+
+	ret = intel_ring_begin(request, 0);
+	if (ret)
+		return ret;
+
+	request->reserved_space -= MIN_SPACE_FOR_ADD_REQUEST;
+	return 0;
 }
 
 static int wait_for_space(struct drm_i915_gem_request *req, int bytes)
-- 
2.8.1