Mir-on-X mouse input is jerky/stuttery compared to Mir-on-KMS

It appears Xorg uses CLOCK_MONOTONIC_COARSE for its (input) timestamps. And Mir generally uses CLOCK_MONOTONIC for its input resampling code (via systemTime and libinput). On top of that, a lot of precision is lost in Xorg only keeping millisecond accuracy by design :(

So those two issues probably explain the jerkiness completely, and especially explains why it's only visible when input resampling is active (because that's the only time we need the clocks to match up).

Brandon has also mentioned he has delay issues with key events (which I am not seeing). But that could also be explained by the above timing problems.

We should try to at least convert X's input event timestamps into CLOCK_MONOTONIC in case the epoch and/or frequencies are different. And as a last resort might want to try just synthesising timestamps in the x11 input platform.

Alternatively, just wait till we have retired Mir's input resampling logic, which should happen in the next month or so. Then we won't notice the problem any more as all events will get delivered unconditionally, regardless of timestamp precision.

Fix committed into lp:mir at revision 3949, scheduled for release in mir, milestone 1.0.0

This bug was fixed in the package mir - 0.26.0+17.04.20170126.3-0ubuntu1

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mir (0.26.0+17.04.20170126.3-0ubuntu1) zesty; urgency=medium

  [ Daniel van Vugt ]
  * New upstream release 0.26.0 (https://launchpad.net/mir/+milestone/0.26.0)
    - ABI summary:
      . mirclient ABI unchanged at 9
      . mirserver ABI bumped to 43
      . mircommon ABI unchanged at 7
      . mirplatform ABI unchanged at 14
      . mirprotobuf ABI unchanged at 3
      . mirplatformgraphics ABI unchanged at 11
      . mirclientplatform ABI unchanged at 5
      . mirinputplatform ABI unchanged at 6
      . mircore ABI unchanged at 1
    - Enhancements:
      . New/improved toolkit APIs: MirInputConfig and related functions,
        MirWindow and related functions, DisplayConfig and related functions,
        MirScreencastSpec and related functions,
      . Support for configuring input configuration
      . Introduce toolkit extension mechanism for platform specific APIs.
      . Toolkit extensions for: mesa_drm_auth, set_gbm_device and
        window_coordinate_translation
      . Screencasting to a specific MirBuffer.
      . Add DisplayConfigurationController::base_configuration() so downstreams
        can get the base configuration. (Weirdly they can already set it.).
      . x11 platform: allow adjustable scale parameter.
      . Added EDID support: client API, server logging and in mirout.
      . mirout: Add newer attributes only available in the new display
        config API: scaling factor, subpixel arrangement and form factor.
      . mirout: Log the orientation and logical size of each output too.
      . Replace the mir::Server-overridable Reports with Observers.
      . Add xkbcommon to mirclient.pc Requires.private.
      . Deprecate legacy toolkit APIs that will be removed in Mir 1.0
      . Introduced 'client-side vsync', which dramatically reduces latency
        from the client to the screen (particularly for nested servers like
        Unity8).
    - Bugs fixed:
      . [performance] Restore support for better-than-triple buffering by
        default. (LP: #1240909)
      . Frame rate is artificially low on Diamondville Intel Atom systems due
        to aggressive power management (LP: #1388490)
      . [testsfail] failure in CI in
        AndroidInputReceiverSetup.slow_raw_input_doesnt_cause_frameskipping
        (LP: #1394369)
      . [trusted prompt sessions] Can't open two prompt sessions at the same
        time (LP: #1494197)
      . Changing scale, formFactor or DPI in display configuration causes
        renderer teardown/recreate unnecessarily (LP: #1556142)
      . [testsfail] ApplicationNotRespondingDetection.failure_to_pong_is_
        noticed (LP: #1570327)
      . CI failure in TestClientInput.receives_one_touch_event_per_frame
        (LP: #1570698)
      . Mir-on-X mouse input is jerky/stuttery compared to Mir-on-KMS
        (LP: #1576600)
      . [regression] Two fingers in mir_proving_server now resizes/moves app
        windows (two finger apps unusable) (LP: #1586311)
      . Pointer/cursor input lag in unity8 session (LP: #1591328)
      . PointerConfinement.test_we_update_our_confined_region_on_a_resize
      ...