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I should have admitted defeat long ago as there has been a rare but persistent error on Sandybridge where semaphore signaling did not propagate to the waiter, leading to a GPU hang. With the work on fence signaling for v4.9, the impact of using CPU driven signaling was greatly reduced wrt to the latency of GPU semaphores, though without logical rings support, the benefit of reordering work to avoid bubbles is not realised (i.e. as it stands fence signaling is just a slower, more costly version of HW semaphores; but works more consistently). As a rough indicator of the difference, with semaphores: Sequential (3 engines, 1 processes): average 5.470us per cycle [expected 4.988us] w/o semaphores: Sequential (3 engines, 1 processes): average 15.771us per cycle [expected 4.923us] In comparison, v3.4: with semaphores: Sequential (3 engines, 1 processes): average 16.066us per cycle [expected 11.842us] w/o semaphores: Sequential (3 engines, 1 processes): average 23.460us per cycle [expected 11.839us] Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=54226 #and 100+ dupes Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Acked-by: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20171120205504.21892-3-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.