man: State the negative aspects of TearFree

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 12 insertions, 5 deletions

diff --git a/man/intel.man b/man/intel.man
index d1ec01ce..d5164495 100644
--- a/man/intel.man
+++ b/man/intel.man
@@ -136,11 +136,18 @@ Default: use UXA (render acceleration)
 .TP
 .BI "Option \*qTearFree\*q \*q" boolean \*q
 Disable or enable TearFree updates. This option forces X to perform all
-rendering to a backbuffer prior to updating the actual display. That update
-is then performed synchronously with the vertical refresh of the display so
-that the entire update is complete before the display starts its refresh.
-That is only one frame is ever visible, preventing an unsightly tear between
-two visible differing frames.
+rendering to a backbuffer prior to updating the actual display. It requires
+an extra memory allocation the same size as a framebuffer, the occasional extra
+copy, and requires Damage tracking update. Thus enabling TearFree requires more
+memory and is slower (reduced throughput) and introduces a small amount of
+output latency, but it should not impact input latency. However, the update to
+the screen is then performed synchronously with the vertical refresh of the
+display so that the entire update is completed before the display starts its
+refresh. That is only one frame is ever visible, preventing an unsightly tear
+between two visible and differing frames. Note that this replicates what the
+compositing manager should be doing, so it is not advisable to enable both.
+However, some compositing managers do cause tearing, and if the outputs are
+rotated, there may will still be tearing without TearFree enabled.
 .IP
 Default: TearFree is disabled.
 .TP