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Currently, if a cache entry is empty, the driver will try to take MRs from larger cache entries. This behavior consumes a lot of memory. In addition, when searching for an mkey in an entry, the entry is locked. When using a multithreaded application with the old behavior, the threads will block each other more often, which can hurt performance as can be seen in the table below. Therefore, avoid it by creating a new mkey when the requested cache entry is empty. The test was performed on a machine with Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz 44 cores. Here are the time measures for allocating MRs of 2^6 pages. The search in the cache started from entry 6. +------------+---------------------+---------------------+ | | Old behavior | New behavior | | +----------+----------+----------+----------+ | | 1 thread | 5 thread | 1 thread | 5 thread | +============+==========+==========+==========+==========+ | 1,000 MRs | 14 ms | 30 ms | 14 ms | 80 ms | +------------+----------+----------+----------+----------+ | 10,000 MRs | 135 ms | 6 sec | 173 ms | 880 ms | +------------+----------+----------+----------+----------+ |100,000 MRs | 11.2 sec | 57 sec | 1.74 sec | 8.8 sec | +------------+----------+----------+----------+----------+ Link: https://lore.kernel.org/r/71af2770c737b936f7b10f457f0ef303ffcf7ad7.1632644527.git.leonro@nvidia.com Signed-off-by: Aharon Landau <aharonl@nvidia.com> Signed-off-by: Leon Romanovsky <leonro@nvidia.com> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
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.