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Consider two tasks that are running in parallel on a pair of engines (vcs0, vcs1), but then must complete on a shared engine (rcs0). To maximise throughput, we want to run the first ready task on rcs0 (i.e. the first task that completes on either of vcs0 or vcs1). When using semaphores, however, we will instead queue onto rcs in submission order. To resolve this incorrect ordering, we want to re-evaluate the priority queue when each of the request is ready. Normally this happens because we only insert into the priority queue requests that are ready, but with semaphores we are inserting ahead of their readiness and to compensate we penalize those tasks with reduced priority (so that tasks that do not need to busywait should naturally be run first). However, given a series of tasks that each use semaphores, the queue degrades into submission fifo rather than readiness fifo, and so to counter this we give a small boost to semaphore users as their dependent tasks are completed (and so we no longer require any busywait prior to running the user task as they are then ready themselves). v2: Fixup irqsave for schedule_lock (Tvrtko) Testcase: igt/gem_exec_schedule/semaphore-codependency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Dmitry Rogozhkin <dmitry.v.rogozhkin@intel.com> Cc: Dmitry Ermilov <dmitry.ermilov@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20190409152922.23894-1-chris@chris-wilson.co.uk |
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| init | ||
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| kernel | ||
| lib | ||
| LICENSES | ||
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| README | ||
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.