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A mirror of the official Linux kernel repository just in case
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Currently the driver is notified of new command frame receipt by CQEs. As part of the CQE processing, the driver upcalls the nvmet_fc transport to deliver the command. nvmet_fc, as part of receiving the command builds out a context for it, where one of the first steps is to allocate memory for the io. When running with tests that do large ios (1MB), it was found on some systems, the total number of outstanding I/O's, at 1MB per, completely consumed the system's memory. Thus additional ios were getting blocked in the memory allocator. Given that this blocked the lpfc thread processing CQEs, there were lots of other commands that were received and which are then held up, and given CQEs are serially processed, the aggregate delays for an IO waiting behind the others became cummulative - enough so that the initiator hit timeouts for the ios. The basic fix is to avoid the direct upcall and instead schedule a work item for each io as it is received. This allows the cq processing to complete very quickly, and each io can then run or block on it's own. However, this general solution hurts latency when there are few ios. As such, implemented the fix such that the driver watches how many CQEs it has processed sequentially in one run. As long as the count is below a threshold, the direct nvmet_fc upcall will be made. Only when the count is exceeded will it revert to work scheduling. Given that debug of this showed a surprisingly long delay in cq processing, the io timer stats were updated to better reflect the processing of the different points. Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com> Signed-off-by: James Smart <jsmart2021@gmail.com> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com> |
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| kernel | ||
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| .get_maintainer.ignore | ||
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| README | ||
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.