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When running igt@gem_exec_balancer@individual for multiple iterations, it is seen that the delta busyness returned by PMU is 0. The issue stems from a combination of 2 implementation specific details: 1) gt_park is throttling __update_guc_busyness_stats() so that it does not hog PCI bandwidth for some use cases. (Ref:59bcdb564b) 2) busyness implementation always returns monotonically increasing counters. (Ref:cf907f6d29) If an application queried an engine while it was active, engine->stats.guc.running is set to true. Following that, if all PM wakeref's are released, then gt is parked. At this time the throttling of __update_guc_busyness_stats() may result in a missed update to the running state of the engine (due to (1) above). This means subsequent calls to guc_engine_busyness() will think that the engine is still running and they will keep updating the cached counter (stats->total). This results in an inflated cached counter. Later when the application runs a workload and queries for busyness, we return the cached value since it is larger than the actual value (due to (2) above) All subsequent queries will return the same large (inflated) value, so the application sees a delta busyness of zero. Fix the issue by resetting the running state of engines each time intel_guc_busyness_park() is called. v2: (Rodrigo) - Use the correct tag in commit message - Drop the redundant wakeref check in guc_engine_busyness() and update commit message Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/13366 Fixes:cf907f6d29("i915/guc: Ensure busyness counter increases motonically") Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com> Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20250123193839.2394694-1-umesh.nerlige.ramappa@intel.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.