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The ack timeout retransmission time is affected by the following two factors: one is packet life time, another is the HCA processing time. Now the default packet lifetime(CMA_IBOE_PACKET_LIFETIME) is 18. That means the minimum ack timeout is 2 seconds (2^(18+1)*4us=2.097seconds). The packet lifetime means the maximum transmission time of packets on the network, 2 seconds is too long. Assume the network is a clos topology with three layers, every packet will pass through five hops of switches. Assume the buffer of every switch is 128MB and the port transmission rate is 25 Gbit/s, the maximum transmission time of the packet is 200ms(128MB*5/25Gbit/s). Add double redundancy, it is less than 500ms. So change the CMA_IBOE_PACKET_LIFETIME to 16, the maximum transmission time of the packet will be about 500+ms, it is long enough. Link: https://lore.kernel.org/r/20221125010026.755-1-lengchao@huawei.com Signed-off-by: Chao Leng <lengchao@huawei.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.