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Future gen reduce the number of bits we will have available to differentiate between contexts, so reduce the lifetime of the ID assignment from that of the context to its current active cycle (i.e. only while it is pinned for use by the HW, will it have a constant ID). This means that instead of a max of 2k allocated contexts (worst case before fun with bit twiddling), we instead have a limit of 2k in flight contexts (minus a few that have been pinned by the kernel or by perf). To reduce the number of contexts id we require, we allocate a context id on first and mark it as pinned for as long as the GEM context itself is, that is we keep it pinned it while active on each engine. If we exhaust our context id space, then we try to reclaim an id from an idle context. In the extreme case where all context ids are pinned by active contexts, we force the system to idle in order to recover ids. We cannot reduce the scope of an HW-ID to an engine (allowing the same gem_context to have different ids on each engine) as in the future we will need to preassign an id before we know which engine the context is being executed on. v2: Improved commentary (Tvrtko) [I tried at least] References: https://bugs.freedesktop.org/show_bug.cgi?id=107788 Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Cc: Michel Thierry <michel.thierry@intel.com> Cc: Michal Wajdeczko <michal.wajdeczko@intel.com> Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20180904153117.3907-1-chris@chris-wilson.co.uk
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.
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.