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Some users complain about RNR errors on the target, when heavy high-priority tasks run on the initiator. After the investigation, we found out that the receive WRs were exhausted, because the initiator could not post them on time. Receive work reqeusts are posted in chunks to reduce the number of hits to the HCA. The WRs are posted in the receive completion handler when the number of free receive buffers reaches the threshold. But on a high-loaded host, receive CQEs processing can be delayed and all receive WRs will be exhausted. In this case, the target will get an RNR error. To avoid this, we post receive WR, as soon as possible and not in a batch. This increases the number of hits to the HCA, but also the common implementation in most of Linux ULPs (e.g. NVMe-oF/RDMA). As a rule of thumb, performance improvements and heuristics are being added to the RDMA core layer or vendors low level drivers and it's about time to align iSER as well. Link: https://lore.kernel.org/r/20211215135721.3662-3-mgurtovoy@nvidia.com Signed-off-by: Sergey Gorenko <sergeygo@nvidia.com> Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com> Reviewed-by: Israel Rukshin <israelr@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.