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There are lots of POSTING_READ alongside each mmio write Op. While
actually this is not necessary. It just bring too much latency since
PCIe read Op is very slow which is of non-posted transaction.
For PCIe device, the mem transaction for strong ordering rules are:
o PCIe mmio write sequence is FIFO. Posted request cannot
pass previous posted request.
o PCIe mmio read will not go ahead of previous write.
Intel graphics doesn't support RO, so we can apply above rules. In
our case, we only need one POSTING_READ at last. This can remove
half of mmio read Op and then the average ring switch performance
is nearly doubled.
Before After
cycles ~970000 ~550000
Signed-off-by: Changbin Du <changbin.du@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
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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.