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03c10f472a
Our forcewake utilisation is split into categories: automatic and manual. Around bare register reads, we look up the right forcewake domain and automatically acquire and release [upon a timer] the forcewake domain. For other access, where we know we require the forcewake across a group of register reads, we manually acquire the forcewake domain and release it at the end. Again, this currently arms the domain timer for a later release. However, looking at some energy utilisation profiles, we have tried to avoid using forcewake [and rely on the natural wake up to post register updates] due to that even keep the fw active for a brief period contributes to a significant power draw [i.e. when the gpu is sleeping with rc6 at high clocks]. But as it turns out, not posting the writes immediately also has unintended consequences, such as not reducing the clocks and so conserving power while busy. As a compromise, let us only arm the domain timer for automatic forcewake usage around bare register access, but immediately release the forcewake when manually acquired by intel_uncore_forcewake_get/_put. The corollary to this is that we may instead have to take forcewake more often, and so incur a latency penalty in doing so. For Sandybridge this was significant, and even on the latest machines, taking forcewake at interrupt frequency is a huge impact. [So we don't do that anymore! Hopefully, this will spare us from still needing the mitigation of the timer for steady state execution.] Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20200601072446.19548-13-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.