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Knowing the round trip time of an engine is useful for tracking the health of the system as well as providing a metric for the baseline responsiveness of the engine. We can use the latter metric for automatically tuning our waits in selftests and when idling so we don't confuse a slower system with a dead one. Upon idling the engine, we send one last pulse to switch the context away from precious user state to the volatile kernel context. We know the engine is idle at this point, and the pulse is non-preemptible, so this provides us with a good measurement of the round trip time. It also provides us with faster engine parking for ringbuffer submission, which is a welcome bonus (e.g. softer-rc6). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Stuart Summers <stuart.summers@intel.com> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20191219105043.4169050-1-chris@chris-wilson.co.uk Link: https://patchwork.freedesktop.org/patch/msgid/20191219124353.8607-2-chris@chris-wilson.co.uk
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.