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To determine whether an engine has 'stuck', we simply check whether or not is still on the same seqno for several seconds. To keep this simple mechanism intact over the loss of a global seqno, we can simply add a new global heartbeat seqno instead. As we cannot know the sequence in which requests will then be completed, we use a primitive random number generator instead (with a cycle long enough to not matter over an interval of a few thousand requests between hangcheck samples). The alternative to using a dedicated seqno on every request is to issue a heartbeat request and query its progress through the system. Sadly this requires us to reduce struct_mutex so that we can issue requests without requiring that bkl. v2: And without the extra CS_STALL for the hangcheck seqno -- we don't need strict serialisation with what comes later, we just need to be sure we don't write the hangcheck seqno before our batch is flushed. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20190226094922.31617-1-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.
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.