Merge branch 'expose-burst-period-for-devlink-health-reporter'

Mark Bloch says:

====================
Expose burst period for devlink health reporter

Shahar writes:
--------------------------------------------------------------------------

Currently, the devlink health reporter initiates the grace period
immediately after recovering an error, which blocks further recovery
attempts until the grace period concludes. Since additional errors
are not generally expected during this short interval, any new error
reported during the grace period is not only rejected but also causes
the reporter to enter an error state that requires manual intervention.

This approach poses a problem in scenarios where a single root cause
triggers multiple related errors in quick succession - for example,
a PCI issue affecting multiple hardware queues. Because these errors
are closely related and occur rapidly, it is more effective to handle
them together rather than handling only the first one reported and
blocking any subsequent recovery attempts. Furthermore, setting the
reporter to an error state in this context can be misleading, as these
multiple errors are manifestations of a single underlying issue, making
it unlike the general case where additional errors are not expected
during the grace period.

To resolve this, introduce a configurable burst period attribute to the
devlink health reporter. This period starts when the first error
is recovered and lasts for a user-defined duration. Once this error
burst period expires, the grace period begins. After the grace period
ends, a new reported error will start the same flow again.

Timeline summary:

----|--------|------------------------------/----------------------/--
error is  error is      burst period             grace period
reported  recovered  (recoveries allowed)     (recoveries blocked)

With burst period, create a time window during which recovery attempts
are permitted, allowing all reported errors to be handled sequentially
before the grace period starts. Once the grace period begins, it
prevents any further error recoveries until it ends.

When burst period is set to 0, current behavior is preserved.

Design alternatives considered:

1. Recover all queues upon any error:
   A brute-force approach that recovers all queues on any error.
   While simple, it is overly aggressive and disrupts unaffected queues
   unnecessarily. Also, because this is handled entirely within the
   driver, it leads to a driver-specific implementation rather than a
   generic one.

2. Per-queue reporter:
   This design would isolate recovery handling per SQ or RQ, effectively
   removing interdependencies between queues. While conceptually clean,
   it introduces significant scalability challenges as the number of
   queues grows, as well as synchronization challenges across multiple
   reporters.

3. Error aggregation with delayed handling:
   Errors arriving during the grace period are saved and processed after
   it ends. While addressing the issue of related errors whose recovery
   is aborted as grace period started, this adds complexity due to
   synchronization needs and contradicts the assumption that no errors
   should occur during a healthy system’s grace period. Also, this
   breaks the important role of grace period in preventing an infinite
   loop of immediate error detection following recovery. In such cases
   we want to stop.

4. Allowing a fixed burst of errors before starting grace period:
   Allows a set number of recoveries before the grace period begins.
   However, it also requires limiting the error reporting window.
   To keep the design simple, the burst threshold becomes redundant.

The burst period design was chosen for its simplicity and precision in
addressing the problem at hand. It effectively captures the temporal
correlation of related errors and aligns with the original intent of
the grace period as a stabilization window where further errors are
unexpected, and if they do occur, they indicate an abnormal system
state.

v3: https://lore.kernel.org/1755111349-416632-1-git-send-email-tariqt@nvidia.com
v2: https://lore.kernel.org/1753390134-345154-1-git-send-email-tariqt@nvidia.com
v1: https://lore.kernel.org/1752768442-264413-1-git-send-email-tariqt@nvidia.com
====================

Link: https://patch.msgid.link/20250824084354.533182-1-mbloch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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