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A request is assigned a global seqno only when it is on the hardware execution queue. The global seqno can be used to maintain a list of requests on the same engine in retirement order, for example for constructing a priority queue for waiting. Prior to its execution, or if it is subsequently removed in the event of preemption, its global seqno is zero. As both insertion and removal from the execution queue may operate in IRQ context, it is not guarded by the usual struct_mutex BKL. Instead those relying on the global seqno must be prepared for its value to change between reads. Only when the request is complete can the global seqno be stable (due to the memory barriers on submitting the commands to the hardware to write the breadcrumb, if the HWS shows that it has passed the global seqno and the global seqno is unchanged after the read, it is indeed complete). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-9-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.