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The irq_seqno_barrier is a tradeoff between doing work on every request (on the GPU) and doing work after every interrupt (on the CPU). We presume we have many more requests than interrupts! However, for Ironlake, the workaround is a pretty hideous usleep() and so even though it was found we need to repeat the MI_STORE_DWORD_IMM 8 times, or about 1us of GPU time, doing so is preferrable than requiring a sleep of 125-250us on the CPU where we desire to respond immediately (ideally from within the interrupt handler)! The additional MI_STORE_DWORD_IMM also have the side-effect of flushing MI operations from userspace which are not caught by MI_FLUSH! Testcase: igt/gem_sync Testcase: igt/gem_exec_whisper Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20181228171641.16531-5-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.