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Michael J. Ruhl 90b2620e6a IB/hfi1: Fix a latency issue for small messages
A recent performance enhancement introduced a latency issue in the
HFI message path.  The new algorithm removed a forced call send for
PIO messages and added a forced schedule event for messages larger
than the MTU.

For PIO, the schedule path can introduce thrashing that can
significantly impact the throughput for small messages.

If a message size is within the PIO threshold, always take the send
path.

Fixes: 0b79b27748 ("IB/{hfi1, qib, rdmavt}: Schedule multi RC/UC packets instead of posting")
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>
History 2018-12-03 16:05:19 -05:00
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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.