[Intel-gfx] [PATCH v3 0/6] Default request/fence expiry + watchdog

[Tvrtko Ursulin]

From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

"Watchdog" aka "restoring hangcheck" aka default request/fence expiry - second
post of a somewhat controversial feature, now upgraded to patch status.

I quote the "watchdog" becuase in classical sense watchdog would allow userspace
to ping it and so remain alive.

I quote "restoring hangcheck" because this series, contrary to the old
hangcheck, is not looking at whether the workload is making any progress from
the kernel side either. (Although disclaimer my memory may be leaky - Daniel
suspects old hangcheck had some stricter, more indiscriminatory, angles to it.
But apart from being prone to both false negatives and false positives I can't
remember that myself.)

Short version - ask is to fail any user submissions after a set time period. In
this RFC that time is twelve seconds.

Time counts from the moment user submission is "runnable" (implicit and explicit
dependencies have been cleared) and keeps counting regardless of the GPU
contetion caused by other users of the system.

So semantics are really a bit weak, but again, I understand this is really
really wanted by the DRM core even if I am not convinced it is a good idea.

There are some dangers with doing this - text borrowed from a patch in the
series:

  This can have an effect that workloads which used to work fine will
  suddenly start failing. Even workloads comprised of short batches but in
  long dependency chains can be terminated.

  And becuase of lack of agreement on usefulness and safety of fence error
  propagation this partial execution can be invisible to userspace even if
  it is "listening" to returned fence status.

  Another interaction is with hangcheck where care needs to be taken timeout
  is not set lower or close to three times the heartbeat interval. Otherwise
  a hang in any application can cause complete termination of all
  submissions from unrelated clients. Any users modifying the per engine
  heartbeat intervals therefore need to be aware of this potential denial of
  service to avoid inadvertently enabling it.

  Given all this I am personally not convinced the scheme is a good idea.
  Intuitively it feels object importers would be better positioned to
  enforce the time they are willing to wait for something to complete.

v2:
 * Dropped context param.
 * Improved commit messages and Kconfig text.

v3:
 * Log timeouts.
 * Bump timeout to 20s to see if it helps Tigerlake.
 * Fix sentinel assert.

Test-with: 20210318162400.2065097-1-tvrtko.ursulin at linux.intel.com
Cc: Daniel Vetter <daniel.vetter at ffwll.ch

Chris Wilson (1):
  drm/i915: Individual request cancellation

Tvrtko Ursulin (5):
  drm/i915: Restrict sentinel requests further
  drm/i915: Handle async cancellation in sentinel assert
  drm/i915: Request watchdog infrastructure
  drm/i915: Fail too long user submissions by default
  drm/i915: Allow configuring default request expiry via modparam

 drivers/gpu/drm/i915/Kconfig.profile          |  14 ++
 drivers/gpu/drm/i915/gem/i915_gem_context.c   |  39 ++++
 .../gpu/drm/i915/gem/i915_gem_context_types.h |   4 +
 drivers/gpu/drm/i915/gt/intel_context_param.h |  11 +-
 drivers/gpu/drm/i915/gt/intel_context_types.h |   4 +
 .../gpu/drm/i915/gt/intel_engine_heartbeat.c  |   1 +
 .../drm/i915/gt/intel_execlists_submission.c  |  18 +-
 .../drm/i915/gt/intel_execlists_submission.h  |   2 +
 drivers/gpu/drm/i915/gt/intel_gt.c            |   3 +
 drivers/gpu/drm/i915/gt/intel_gt.h            |   2 +
 drivers/gpu/drm/i915/gt/intel_gt_requests.c   |  26 +++
 drivers/gpu/drm/i915/gt/intel_gt_types.h      |   7 +
 drivers/gpu/drm/i915/i915_params.c            |   5 +
 drivers/gpu/drm/i915/i915_params.h            |   1 +
 drivers/gpu/drm/i915/i915_request.c           | 108 +++++++++-
 drivers/gpu/drm/i915/i915_request.h           |  12 +-
 drivers/gpu/drm/i915/selftests/i915_request.c | 201 ++++++++++++++++++
 17 files changed, 450 insertions(+), 8 deletions(-)

-- 
2.27.0