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Typical SLI-4 hardware supports up to 2 4KB pages to be registered per XRI to contain the exchanges Scatter/Gather List. This caps the number of SGL elements that can be in the SGL. There are not extensions to extend the list out of the 2 pages. The G7 hardware adds a SGE type that allows the SGL to be vectored to a different scatter/gather list segment. And that segment can contain a SGE to go to another segment and so on. The initial segment must still be pre-registered for the XRI, but it can be a much smaller amount (256Bytes) as it can now be dynamically grown. This much smaller allocation can handle the SG list for most normal I/O, and the dynamic aspect allows it to support many MB's if needed. The implementation creates a pool which contains "segments" and which is initially sized to hold the initial small segment per xri. If an I/O requires additional segments, they are allocated from the pool. If the pool has no more segments, the pool is grown based on what is now needed. After the I/O completes, the additional segments are returned to the pool for use by other I/Os. Once allocated, the additional segments are not released under the assumption of "if needed once, it will be needed again". Pools are kept on a per-hardware queue basis, which is typically 1:1 per cpu, but may be shared by multiple cpus. The switch to the smaller initial allocation significantly reduces the memory footprint of the driver (which only grows if large ios are issued). Based on the several K of XRIs for the adapter, the 8KB->256B reduction can conserve 32MBs or more. It has been observed with per-cpu resource pools that allocating a resource on CPU A, may be put back on CPU B. While the get routines are distributed evenly, only a limited subset of CPUs may be handling the put routines. This can put a strain on the lpfc_put_cmd_rsp_buf_per_cpu routine because all the resources are being put on a limited subset of CPUs. 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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| Documentation | ||
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| include | ||
| init | ||
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| kernel | ||
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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.