[PATCH 10/20] drm/i915: Optimization to reduce the sampling time of GuC log buffer

[akash.goel at intel.com]

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

GuC firmware sends an interrupt to flush the log buffer when it becomes
half full, so Driver doesn't really need to sample the complete buffer
and can just copy only the newly written data by GuC into the local
buffer, i.e. as per the read & write pointer values.
Moreover the flush interrupt would generally come for one type of log
buffer, when it becomes half full, so at that time the other 2 types of
log buffer would comparatively have much lesser unread data in them.
In case of overflow reported by GuC, Driver do need to copy the entire
buffer as the whole buffer would contain the unread data.

v2: Rebase.

Signed-off-by: Akash Goel <akash.goel at intel.com>
---
 drivers/gpu/drm/i915/i915_guc_submission.c | 40 +++++++++++++++++++++++++-----
 1 file changed, 34 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
index 42252e6..230a137 100644
--- a/drivers/gpu/drm/i915/i915_guc_submission.c
+++ b/drivers/gpu/drm/i915/i915_guc_submission.c
@@ -874,7 +874,8 @@ static void guc_read_update_log_buffer(struct intel_guc *guc)
 	struct guc_log_buffer_state *log_buffer_state, *log_buffer_snapshot_state;
 	struct guc_log_buffer_state log_buffer_state_local;
 	void *src_data_ptr, *dst_data_ptr;
-	u32 i, buffer_size;
+	bool new_overflow;
+	u32 i, buffer_size, read_offset, write_offset, bytes_to_copy;
 
 	if (!guc->log.buf_addr)
 		return;
@@ -897,10 +898,13 @@ static void guc_read_update_log_buffer(struct intel_guc *guc)
 		memcpy(&log_buffer_state_local, log_buffer_state,
 				sizeof(struct guc_log_buffer_state));
 		buffer_size = log_buffer_state_local.size;
+		read_offset = log_buffer_state_local.read_ptr;
+		write_offset = log_buffer_state_local.sampled_write_ptr;
 
 		guc->log.flush_count[i] += log_buffer_state_local.flush_to_file;
 		if (log_buffer_state_local.buffer_full_cnt !=
 					guc->log.prev_overflow_count[i]) {
+			new_overflow = 1;
 			guc->log.total_overflow_count[i] +=
 				(log_buffer_state_local.buffer_full_cnt -
 				 guc->log.prev_overflow_count[i]);
@@ -914,7 +918,8 @@ static void guc_read_update_log_buffer(struct intel_guc *guc)
 			guc->log.prev_overflow_count[i] =
 					log_buffer_state_local.buffer_full_cnt;
 			DRM_ERROR_RATELIMITED("GuC log buffer overflow\n");
-		}
+		} else
+			new_overflow = 0;
 
 		if (log_buffer_snapshot_state) {
 			/* First copy the state structure in local buffer */
@@ -926,13 +931,37 @@ static void guc_read_update_log_buffer(struct intel_guc *guc)
 			 * for consistency set the write pointer value to same
 			 * value of sampled_write_ptr in the snapshot buffer.
 			 */
-			log_buffer_snapshot_state->write_ptr =
-				log_buffer_snapshot_state->sampled_write_ptr;
+			log_buffer_snapshot_state->write_ptr = write_offset;
 
 			log_buffer_snapshot_state++;
 
 			/* Now copy the actual logs */
 			memcpy(dst_data_ptr, src_data_ptr, buffer_size);
+			if (unlikely(new_overflow)) {
+				/* copy the whole buffer in case of overflow */
+				read_offset = 0;
+				write_offset = buffer_size;
+			} else if (unlikely((read_offset > buffer_size) ||
+					    (write_offset > buffer_size))) {
+				DRM_ERROR("invalid log buffer state\n");
+				/* copy whole buffer as offsets are unreliable */
+				read_offset = 0;
+				write_offset = buffer_size;
+			}
+
+			/* Just copy the newly written data */
+			if (read_offset <= write_offset) {
+				bytes_to_copy = write_offset - read_offset;
+				memcpy(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,
+				     src_data_ptr + read_offset, bytes_to_copy);
+
+				bytes_to_copy = write_offset;
+				memcpy(dst_data_ptr, src_data_ptr, bytes_to_copy);
+			}
 
 			src_data_ptr += buffer_size;
 			dst_data_ptr += buffer_size;
@@ -941,8 +970,7 @@ static void guc_read_update_log_buffer(struct intel_guc *guc)
 		/* FIXME: invalidate/flush for log buffer needed */
 
 		/* Update the read pointer in the shared log buffer */
-		log_buffer_state->read_ptr =
-			log_buffer_state_local.sampled_write_ptr;
+		log_buffer_state->read_ptr = write_offset;
 
 		/* Clear the 'flush to file' flag */
 		log_buffer_state->flush_to_file = 0;
-- 
1.9.2