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On gen9+, after an idle period the HW will disable the entire power well to conserve power (by preventing current leakage). It takes around a 100 microseconds to bring the power well back online afterwards. With the current hysteresis value of 25us (really 25 * 1280ns), we do not have sufficient time to respond to an interrupt and schedule the next execution before the HW powers itself down. (At present, we prevent this by grabbing the forcewake for prolonged periods of time, but that overkill fixed in the next patch.) The minimum we want to set the power gating hysteresis to is the length of time it takes us to service the GPU, which across a broad spectrum of machines is about 250us. (Note this also brings guc latency into the same ballpark as execlists.) v2: Include some notes on where I plucked the numbers from. Testcase: igt/gem_exec_nop/sequential Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Michal Wajdeczko <michal.wajdeczko@intel.com> Cc: Sagar Arun Kamble <sagar.a.kamble@intel.com> Cc: Michel Thierry <michel.thierry@intel.com> Cc: Michal Winiarski <michal.winiarski@intel.com> Reviewed-by: Sagar Arun Kamble <sagar.a.kamble@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20180122135541.32222-1-chris@chris-wilson.co.uk |
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. 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.