[PATCH v4 0/3] drm/xe: fix GuC TLB invalidation ack stalls on ARL (Wa_22016122933)

["Tales A. Mendonça" <talesam@gmail.com>]

Hi,

v4 of the TLB invalidation ack stall fix for ARL, rebased on today's
drm-tip. Tracked in:

  https://gitlab.freedesktop.org/drm/xe/kernel/-/work_items/8678

Recap: on the standalone media GT of MTL/ARL the CPU reads stale cache
lines for data the GuC has already written. The visible symptom is TLB
invalidation acks appearing to stall for a near-constant ~2.3s. i915
works around this as Wa_22016122933; xe never inherited it. Patch 3
implements it, scoped like i915.

In v3 I asked two open questions in this cover letter. Since there was
no preference expressed, v4 makes the conservative choice in both cases
and documents the reasoning in the commit message, so the series is not
blocked on a decision:

 1. CPU mapping: keeping XE_BO_FLAG_NEEDS_UC (uncached on both sides).
    It is the tested configuration and no throughput difference against
    the CPU-WC variant was measurable. Matching i915's exact CPU-WC +
    GGTT-UC combination needs either a new BO flag or decoupling the
    GGTT cache-mode selection from XE_BO_FLAG_NEEDS_UC; happy to add
    that plumbing if parity is preferred.

 2. Scope: covering the GuC-shared allocations (CTBs, log, ADS, SLPC,
    engine activity), which is where the failures were observed. i915
    additionally covers media-GT LRC/ring state; that can be a
    follow-up if wanted.

Fixes:/Cc: stable are still left out, since MTL/ARL is require_force_probe
in xe. Also happy to add them.

Validation of patch 3 is now six weeks on two ARL machines (7d51 and
7dd1), across kernels 7.1.6, 7.1.8 and 7.2, with over 10M TLB
invalidations processed and zero ack stalls. Before the fix both
machines reproduced 20-60 stalls/day, every day, on two GuC firmware
versions. The 7dd1 machine, which could not survive a day of media
workloads on xe without a platform freeze, has been running xe full
time since 11 August with zero incidents.

Patches 1-2 are the diagnostics that made the investigation possible
and are unchanged since v3. checkpatch is clean on the series.

v3 -> v4:
- Rebased on drm-tip.
- Patch 3: resolved both open questions in the commit message instead
  of leaving them for discussion; refreshed validation data.

Thanks,
Tales

Tales A. Mendonça (3):
  drm/xe: Capture devcoredump on TLB invalidation timeout
  drm/xe: Log when a timed out TLB invalidation ack finally arrives
  drm/xe: Implement Wa_22016122933

 drivers/gpu/drm/xe/xe_devcoredump.c         | 46 +++++++++++----------
 drivers/gpu/drm/xe/xe_devcoredump.h         | 15 +++++--
 drivers/gpu/drm/xe/xe_guc.c                 | 16 +++++++
 drivers/gpu/drm/xe/xe_guc.h                 |  2 +
 drivers/gpu/drm/xe/xe_guc_ads.c             |  3 +-
 drivers/gpu/drm/xe/xe_guc_ct.c              |  6 ++-
 drivers/gpu/drm/xe/xe_guc_engine_activity.c |  6 ++-
 drivers/gpu/drm/xe/xe_guc_log.c             |  7 +++-
 drivers/gpu/drm/xe/xe_guc_pc.c              |  3 +-
 drivers/gpu/drm/xe/xe_tlb_inval.c           | 39 +++++++++++++++++
 drivers/gpu/drm/xe/xe_tlb_inval_types.h     | 17 ++++++++
 drivers/gpu/drm/xe/xe_wa_oob.rules          |  1 +
 12 files changed, 128 insertions(+), 33 deletions(-)

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2.55.0