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i915_gem_suspend() is called from all of our finalization paths (suspend, hibernate, unload). i915_gem_drain_freed_objects() adds an arbitrary delay as it uses an rcu_barrier() to ensure that there are no more freed objects in flight, and this delay causes a large amount of variability in suspend timings. For S3 suspend, we do not need to free pages as doing so does not impact at all upon the system in its suspended state, unlike S4 hibernation where we do want the hibernation image to be as small as possible. Therefore we can forgo waiting inside i915_gem_suspend(), so long as we ensure that we do cleanup before unload (see i915_gem_load_cleanup()) and prefer to reap our objects prior to hibernation (see i915_gem_freeze()). Removing the rcu_barrier() from i915_gem_suspend() improves S3 latency by about 30ms on Skylake (ymmv). Reported-by: David Weinehall <david.weinehall@linux.intel.com> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: David Weinehall <david.weinehall@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170627173731.11566-1-chris@chris-wilson.co.uk Tested-by: David Weinehall <david.weinehall@linux.intel.com> Reviewed-by: David Weinehall <david.weinehall@linux.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.