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Mike Marciniszyn b58fc80497 IB/hfi1: Eliminate synchronize_rcu() in mr delete
The synchronize_rcu() call can be eliminated to improve memory deregistration
performance.

There are two key fields involved:
- The rcu pointer itself
- the lkey_published field

To close the window between the rcu read of the mregion pointer and the
reference count the code should:

1. To lkey/rkey validation (reader)

Read the rcu pointer.  If the pointer is non-NULL, get a reference.

To the current validation tests use a READ_ONCE() on the lkey_published.

Upon any failure release the reference.

2. To the remove logic (delete)

Insure the published is zeroed prior to setting the pointer to NULL.
This requires using rcu_assign_pointer() to insure lkey_published
is written prior to the NULL.

3. To the insert logic (add)

Insure the published is set use an rcu_assign_pointer() to insure the
pointer is after all MR fields.

Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>
History 2017-04-05 14:45:09 -04:00
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README

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.