9f473ecfe7
As Chris has discovered on his Ivybridge, and later automated test runs have confirmed, on most of our platforms hrtimer faced with heavy GPU load can occasionally become sufficiently imprecise to affect PMU sampling calculations. This means we cannot assume sampling frequency is what we asked for, but we need to measure the interval ourselves. This patch is similar to Chris' original proposal for per-engine counters, but instead of introducing a new set to work around the problem with frequency sampling, it swaps around the way internal frequency accounting is done. Instead of accumulating current frequency and dividing by sampling frequency on readout, it accumulates frequency scaled by each period. v2: * Typo in commit message, comment on period calculation and USEC_PER_SEC. (Chris Wilson) Testcase: igt/perf_pmu/*busy* # snb, ivb, hsw Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Suggested-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> Link: https://patchwork.freedesktop.org/patch/msgid/20180605140253.3541-1-tvrtko.ursulin@linux.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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.