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The engine also provides a mirror of the CSB write pointer in the HWSP, but not of our read pointer. To take advantage of this we need to remember where we read up to on the last interrupt and continue off from there. This poses a problem following a reset, as we don't know where the hw will start writing from, and due to the use of power contexts we cannot perform that query during the reset itself. So we continue the current modus operandi of delaying the first read of the context-status read/write pointers until after the first interrupt. With this we should now have eliminated all uncached mmio reads in handling the context-status interrupt, though we still have the uncached mmio writes for submitting new work, and many uncached mmio reads in the global interrupt handler itself. Still a step in the right direction towards reducing our resubmit latency, although it appears lost in the noise! v2: Cannonlake moved the CSB write index v3: Include the sw/hwsp state in debugfs/i915_engine_info v4: Also revert to using CSB mmio for GVT-g v5: Prevent the compiler reloading tail (Mika) Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Michel Thierry <michel.thierry@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com> Cc: Zhenyu Wang <zhenyuw@linux.intel.com> Cc: Zhi Wang <zhi.a.wang@intel.com> Acked-by: Michel Thierry <michel.thierry@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20170913085605.18299-6-chris@chris-wilson.co.uk Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
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.