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During igt, we frequently call into the driver to reset both HW and driver state (idling the device, waiting for it to become idle and freeing off old objects) to ensure that we start each test/subtest/pass from known state. This process incurs an RCU barrier or two to ensure that any such pending frees are indeed flushed before we return. However, unconditionally waiting on the RCU barrier adds needless delay to many callers, which adds up to several seconds when repeated thousands of times. We can skip the rcu_barrier() if by tracking how many outstanding frees we have, we know there are none. The same path is used along suspend, where we may be able to save the unconditional RCU barrier. To put it into perspective with a completely meaningless microbenchmark, igt/gem_sync/idle is improved from 50ms to 30us on bdw. v2: Remove the extra synchronize_rcu() inside i915_drop_caches_set() Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20180219220631.25001-1-chris@chris-wilson.co.uk
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.