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  1. 04 5月, 2019 4 次提交
    • C
      drm/i915: Disable semaphore busywaits on saturated systems · ca6e56f6
      由 Chris Wilson 提交于 
      Asking the GPU to busywait on a memory address, perhaps not unexpectedly
in hindsight for a shared system, leads to bus contention that affects
CPU programs trying to concurrently access memory. This can manifest as
a drop in transcode throughput on highly over-saturated workloads.

The only clue offered by perf, is that the bus-cycles (perf stat -e
bus-cycles) jumped by 50% when enabling semaphores. This corresponds
with extra CPU active cycles being attributed to intel_idle's mwait.

This patch introduces a heuristic to try and detect when more than one
client is submitting to the GPU pushing it into an oversaturated state.
As we already keep track of when the semaphores are signaled, we can
inspect their state on submitting the busywait batch and if we planned
to use a semaphore but were too late, conclude that the GPU is
overloaded and not try to use semaphores in future requests. In
practice, this means we optimistically try to use semaphores for the
first frame of a transcode job split over multiple engines, and fail if
there are multiple clients active and continue not to use semaphores for
the subsequent frames in the sequence. Periodically, we try to
optimistically switch semaphores back on whenever the client waits to
catch up with the transcode results.

With 1 client, on Broxton J3455, with the relative fps normalized by %cpu:

x no semaphores
+ drm-tip
* patched
+------------------------------------------------------------------------+
|                                                    *                   |
|                                                    *+                  |
|                                                    **+                 |
|                                                    **+  x              |
|                                x               *  +**+  x              |
|                                x  x       *    *  +***x xx             |
|                                x  x       *    * *+***x *x             |
|                                x  x*   +  *    * *****x *x x           |
|                         +    x xx+x*   + ***   * ********* x   *       |
|                         +    x xx+x*   * *** +** ********* xx  *       |
|    *   +         ++++*  +    x*x****+*+* ***+*************+x*  *       |
|*+ +** *+ + +* + *++****** *xxx**********x***+*****************+*++    *|
|                                   |__________A_____M_____|             |
|                           |_______________A____M_________|             |
|                                 |____________A___M________|            |
+------------------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x 120       2.60475       3.50941       3.31123     3.2143953    0.21117399
+ 120        2.3826       3.57077       3.25101     3.1414161    0.28146407
Difference at 95.0% confidence
	-0.0729792 +/- 0.0629585
	-2.27039% +/- 1.95864%
	(Student's t, pooled s = 0.248814)
* 120       2.35536       3.66713        3.2849     3.2059917    0.24618565
No difference proven at 95.0% confidence

With 10 clients over-saturating the pipeline:

x no semaphores
+ drm-tip
* patched
+------------------------------------------------------------------------+
|                     ++                                        **       |
|                     ++                                        **       |
|                     ++                                        **       |
|                     ++                                        **       |
|                     ++                                    xx ***       |
|                     ++                                    xx ***       |
|                     ++                                    xxx***       |
|                     ++                                    xxx***       |
|                    +++                                    xxx***       |
|                    +++                                    xx****       |
|                    +++                                    xx****       |
|                    +++                                    xx****       |
|                    +++                                    xx****       |
|                    ++++                                   xx****       |
|                   +++++                                   xx****       |
|                   +++++                                 x x******      |
|                  ++++++                                 xxx*******     |
|                  ++++++                                 xxx*******     |
|                  ++++++                                 xxx*******     |
|                  ++++++                                 xx********     |
|                  ++++++                               xxxx********     |
|                  ++++++                               xxxx********     |
|                ++++++++                             xxxxx*********     |
|+ +  +        + ++++++++                           xxx*xx**********x*  *|
|                                                         |__A__|        |
|                 |__AM__|                                               |
|                                                            |__A_|      |
+------------------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x 120       2.47855        2.8972       2.72376     2.7193402   0.074604933
+ 120       1.17367       1.77459       1.71977     1.6966782   0.085850697
Difference at 95.0% confidence
	-1.02266 +/- 0.0203502
	-37.607% +/- 0.748352%
	(Student's t, pooled s = 0.0804246)
* 120       2.57868       3.00821       2.80142     2.7923878   0.058646477
Difference at 95.0% confidence
	0.0730476 +/- 0.0169791
	2.68622% +/- 0.624383%
	(Student's t, pooled s = 0.0671018)

Indicating that we've recovered the regression from enabling semaphores
on this saturated setup, with a hint towards an overall improvement.

Very similar, but of smaller magnitude, results are observed on both
Skylake(gt2) and Kabylake(gt4). This may be due to the reduced impact of
bus-cycles, where we see a 50% hit on Broxton, it is only 10% on the big
core, in this particular test.

One observation to make here is that for a greedy client trying to
maximise its own throughput, using semaphores is the right choice. It is
only the holistic system-wide view that semaphores of one client
impacts another and reduces the overall throughput where we would choose
to disable semaphores.

The most noticeable negactive impact this has is on the no-op
microbenchmarks, which are also very notable for having no cpu bus load.
In particular, this increases the runtime and energy consumption of
gem_exec_whisper.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Dmitry Rogozhkin <dmitry.v.rogozhkin@intel.com>
Cc: Dmitry Ermilov <dmitry.ermilov@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190504070707.30902-1-chris@chris-wilson.co.uk
      ca6e56f6
    • V
      drm/i915: Use mul_u32_u32() more · d492a29d
      由 Ville Syrjälä 提交于 
      We have a lot of '(u64)foo * bar' everywhere. Replace with
mul_u32_u32() to avoid gcc failing to use a regular 32x32->64
multiply for this.
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190408152702.4153-1-ville.syrjala@linux.intel.comReviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
      d492a29d
    • V
      drm/i915: Allow ICL pipe "HDR mode" when the cursor is visible · b7ffc4a8
      由 Ville Syrjälä 提交于 
      Turns out the cursor is compatible with the pipe "HDR mode". It's
only the actual SDR planes that get entirely bypassed during
blending. So let's ignore the cursor when checking if we have
any planes active that aren't HDR compatible. This fixes the
regressions in the kms_cursor_crc and kms_plane_cursor tests.

Cc: Uma Shankar <uma.shankar@intel.com>
Cc: Shashank Sharma <shashank.sharma@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110579
Fixes: 09b25812 ("drm/i915: Enable pipe HDR mode on ICL if only HDR planes are used")
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190502200607.14504-2-ville.syrjala@linux.intel.comReviewed-by: NUma Shankar <uma.shankar@intel.com>
      b7ffc4a8
    • V
      drm/i915: Move the PIPEMISC write the correct place · a832d357
      由 Ville Syrjälä 提交于 
      I fumbled the PIPEMISC write into the wrong place. It only gets
called for fastsets, but since value needs to be updated based on
the set of active planes it needs to be done for all plane updates.
Move it to the correct spot.

The symptoms include SDR planes never showing up if a previous
modeset/fastset left the pipe in HDR mode. This was immediately
obvious when running the kms_plane pixel format tests. Unfortunately
the test didn't realize it was scanning out pure black all the time
and declared success anyway.

Cc: Uma Shankar <uma.shankar@intel.com>
Cc: Shashank Sharma <shashank.sharma@intel.com>
Fixes: 09b25812 ("drm/i915: Enable pipe HDR mode on ICL if only HDR planes are used")
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190502200607.14504-1-ville.syrjala@linux.intel.comReviewed-by: NUma Shankar <uma.shankar@intel.com>
      a832d357
  3. 03 5月, 2019 20 次提交
  5. 02 5月, 2019 8 次提交
  7. 01 5月, 2019 3 次提交
  9. 30 4月, 2019 5 次提交