[PATCH 18/20] drm/i915: Use SSE4.1 movntdqa based memcpy for sampling GuC log buffer

[akash.goel at intel.com]

From: Akash Goel <akash.goel at intel.com>

In order to have fast reads from the GuC log buffer, used SSE4.1 movntdqa
based memcpy function i915_memcpy_from_wc.
GuC log buffer has a WC type vmalloc mapping and copying using movntqda from
WC type memory is almost as fast as reading from WB memory.
This will further reduce the log buffer sampling time, so is needed dearly
to deal with the flush interrupt storm when GuC is generating logs at a very
high rate.
Ideally SSE 4.1 should be present on all chipsets supporting GuC based
submisssions, but if not then logging will not be enabled.

Suggested-by: Chris Wilson <chris at chris-wilson.co.uk>
Signed-off-by: Akash Goel <akash.goel at intel.com>
---
 drivers/gpu/drm/i915/i915_guc_submission.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
index 068a8f2..102f836 100644
--- a/drivers/gpu/drm/i915/i915_guc_submission.c
+++ b/drivers/gpu/drm/i915/i915_guc_submission.c
@@ -972,15 +972,16 @@ static void guc_read_update_log_buffer(struct intel_guc *guc)
 			/* Just copy the newly written data */
 			if (read_offset <= write_offset) {
 				bytes_to_copy = write_offset - read_offset;
-				memcpy(dst_data_ptr + read_offset,
+				i915_memcpy_from_wc(dst_data_ptr + read_offset,
 				     src_data_ptr + read_offset, bytes_to_copy);
 			} else {
 				bytes_to_copy = buffer_size - read_offset;
-				memcpy(dst_data_ptr + read_offset,
+				i915_memcpy_from_wc(dst_data_ptr + read_offset,
 				     src_data_ptr + read_offset, bytes_to_copy);
 
 				bytes_to_copy = write_offset;
-				memcpy(dst_data_ptr, src_data_ptr, bytes_to_copy);
+				i915_memcpy_from_wc(dst_data_ptr, src_data_ptr,
+				     bytes_to_copy);
 			}
 
 			src_data_ptr += buffer_size;
@@ -1195,6 +1196,16 @@ static void guc_create_log(struct intel_guc *guc)
 
 	obj = guc->log.obj;
 	if (!obj) {
+		/* We require SSE 4.1 for fast reads from the GuC log buffer and
+		 * it should be present on the chipsets supporting GuC based
+		 * submisssions.
+		 */
+		if (WARN_ON(!i915_memcpy_from_wc(NULL, NULL, 0))) {
+			/* logging will not be enabled */
+			i915.guc_log_level = -1;
+			return;
+		}
+
 		obj = gem_allocate_guc_obj(dev_priv, size);
 		if (!obj) {
 			/* logging will be off */
-- 
1.9.2