[PATCH v5 0/6] A few drm_syncobj optimisations

[Tvrtko Ursulin]

A small set of drm_syncobj optimisations which should make things a tiny bit
more efficient on the CPU side of things.

Improvement seems to be around 1.5%* more FPS if observed with "vkgears
-present-mailbox" on a Steam Deck Plasma desktop, but I am reluctant to make a
definitive claim on the numbers since there is some run to run variance. But, as
suggested by Michel Dänzer, I did do a five ~100 second runs on the each kernel
to be able to show the ministat analysis.

x before
+ after
+------------------------------------------------------------+
|                          x         +                       |
|                   x      x         +                       |
|                   x      xx      ++++                      |
|                 x x      xx x    ++++                      |
|                 x xx   x xx x+   ++++                      |
|                xxxxx   xxxxxx+   ++++ + +                  |
|                xxxxxxx xxxxxx+x  ++++ +++                  |
|              x xxxxxxxxxxx*xx+* x++++++++   ++             |
|        x x   xxxxxxxxxxxx**x*+*+*++++++++ ++++ +           |
|       xx x   xxxxxxxxxx*x****+***+**+++++ ++++++           |
|x     xxx x   xxxxx*x****x***********+*++**+++++++   +  +  +|
|               |_______A______|                             |
|                             |______A_______|               |
+------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x 135      21697.58     22809.467     22321.396     22307.707     198.75011
+ 118     22200.746      23277.09       22661.4     22671.442     192.10609
Difference at 95.0% confidence
    363.735 +/- 48.3345
    1.63054% +/- 0.216672%
    (Student's t, pooled s = 195.681)

Or when tested on Intel Alderlake, KDE Wayland:

x base
+ syncobj
+--------------------------------------------------------------+
|                                                       +      |
|                                                       +   +  |
|                                                       +   +  |
|                                                       +  ++  |
|                                                       ++ ++  |
|                                       x               ++ ++  |
|                       x               x             + ++ ++  |
|                       x          xx   xx x x        +++++++  |
|                       x   x   xx xxx xxxx*xxx      +++++++++ |
|x       xx x  x    x  xx xxxxxxxxxx*xxx****xxx  +x+ ++++++++++|
|                      |__________A_M_______|     |____A_M___| |
+--------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x  55      7158.232      8058.753      7803.506     7754.5195     191.69526
+  55       7801.23      8272.271      8172.435     8150.6303     105.84085
Difference at 95.0% confidence
    396.111 +/- 57.8717
    5.10813% +/- 0.746296%
    (Student's t, pooled s = 154.838)

Scores may seem low but I had to fix to conservative CPU freq to avoid some
pretty strong thermal throttling causing wild swings within a run. Nevertheless
the improvement is clearly shown here as well.

v2:
 * Implemented review feedback - see patch change logs.

v3:
 * Moved #define DRM_SYNCOBJ_FAST_PATH_ENTRIES one patch earlier for less churn.

 v3.1:
 * Consolidated testing results.

v4:
 * Kernel test robot reports 32-bit ARM does not implement 64-bit get/put_user.
   Switch to copy_to/from_user in relevant places.

v5:
 * Fixed copy_from_user argument order mixup.

Cc: Maíra Canal <mcanal at igalia.com>

Tvrtko Ursulin (6):
  drm/syncobj: Remove unhelpful helper
  drm/syncobj: Do not allocate an array to store zeros when waiting
  drm/syncobj: Avoid one temporary allocation in drm_syncobj_array_find
  drm/syncobj: Avoid temporary allocation in
    drm_syncobj_timeline_signal_ioctl
  drm/syncobj: Add a fast path to drm_syncobj_array_wait_timeout
  drm/syncobj: Add a fast path to drm_syncobj_array_find

 drivers/gpu/drm/drm_syncobj.c | 277 ++++++++++++++++++----------------
 1 file changed, 147 insertions(+), 130 deletions(-)

-- 
2.48.0