[PATCH v6 15/25] drm/i915: Preallocate enough space for the average request

Chris Wilson
2016-04-26T20:06:51Z

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@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
---
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 01517dd7069b..b5c2c1931a5f 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)
goto err_unpin;

+ request->reserved_space -= MIN_SPACE_FOR_ADD_REQUEST;
return 0;

err_unpin:
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 1193372f74fd..1285605f25c7 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)