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When tick values are large, the multiplication by NSEC_PER_SEC is larger than 64 bits and results in bad conversions. The issue is seen in PMU busyness counters that look like they have wrapped around due to bad conversion. i915 PMU implementation returns monotonically increasing counters. If a count is lesser than previous one, it will only return the larger value until the smaller value catches up. The user will see this as zero delta between two measurements even though the engines are busy. Fix it by using mul_u64_u32_div() Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/14955 Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com> Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com> Link: https://lore.kernel.org/r/20251016000350.1152382-2-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 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.