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On DG2, capturing OA reports while running heavy render workloads sometimes results in invalid OA reports where 64-byte chunks inside reports have stale values. Under memory pressure, high OA sampling rates (13.3 us) and heavy render workload, occasionally, the OA HW TAIL pointer does not progress as fast as the sampling rate. When these glitches occur, the TAIL pointer takes approx. 200us to progress. While this is expected behavior from the HW perspective, invalid reports are not expected. In oa_buffer_check_unlocked(), when we execute the if condition, we are updating the oa_buffer.tail to the aging tail and then setting pollin based on this tail value, however, we do not have a chance to rewind and validate the reports prior to setting pollin. The validation happens in a subsequent call to oa_buffer_check_unlocked(). If a read occurs before this validation, then we end up reading reports up until this oa_buffer.tail value which includes invalid reports. Though found on DG2, this affects all platforms. The aging tail logic is no longer necessary since we are explicitly checking for landed reports. Start by dropping the aging tail logic. v2: - Drop extra blank line - Add reason to drop aging logic (Ashutosh) - Add bug links (Ashutosh) - rename aged_tail to read_tail - Squash patches 3 and 1 v3: (Ashutosh) - Remove extra spaces - Remove gtt_offset from the pollin calculation - s/Bug:/Link/ in commit message (checkpatch) Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/7484 Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/7757 Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com> Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20230605193923.1836048-2-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 Restructured Text 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.