libdrm: reduce number of reallocations in drmModeAtomicAddProperty

When calling drmModeAtomicAddProperty allocation of memory
happens as needed in increments of 16 elements. This can be very
slow if there are multiple properties to be updated in an Atomic
Commit call.

Increase this to as many as can fit in a memory PAGE to avoid
having to reallocate memory too often.

Also this patch has a small one line perf tweak in
drmModeAtomicDuplicate() to only memcpy items to the cursor
position in order avoid copying the entire item array if its
mostly empty.

Cc: Sean Paul <seanpaul@chromium.org>
Cc: Alistair Strachan <astrachan@google.com>
Cc: Marissa Wall <marissaw@google.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
[jstultz: Expanded commit message]
Signed-off-by: John Stultz <john.stultz@linaro.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/xf86drmMode.c b/xf86drmMode.c
index 8f8633ed..c878d9ea 100644
--- a/xf86drmMode.c
+++ b/xf86drmMode.c
@@ -1259,7 +1259,7 @@ drm_public drmModeAtomicReqPtr drmModeAtomicDuplicate(drmModeAtomicReqPtr old)
 			return NULL;
 		}
 		memcpy(new->items, old->items,
-		       old->size_items * sizeof(*new->items));
+		       old->cursor * sizeof(*new->items));
 	} else {
 		new->items = NULL;
 	}
@@ -1322,12 +1322,13 @@ drm_public int drmModeAtomicAddProperty(drmModeAtomicReqPtr req,
 		return -EINVAL;
 
 	if (req->cursor >= req->size_items) {
+		const uint32_t item_size_inc = getpagesize() / sizeof(*req->items);
 		drmModeAtomicReqItemPtr new;
 
-		req->size_items += 16;
+		req->size_items += item_size_inc;
 		new = realloc(req->items, req->size_items * sizeof(*req->items));
 		if (!new) {
-			req->size_items -= 16;
+			req->size_items -= item_size_inc;
 			return -ENOMEM;
 		}
 		req->items = new;