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When SCSI-MQ is enabled, the SCSI-MQ layers will do pre-allocation of MQ resources based on shost values set by the driver. In newer cases of the driver, which attempts to set nr_hw_queues to the cpu count, the multipliers become excessive, with a single shost having SCSI-MQ pre-allocation reaching into the multiple GBytes range. NPIV, which creates additional shosts, only multiply this overhead. On lower-memory systems, this can exhaust system memory very quickly, resulting in a system crash or failures in the driver or elsewhere due to low memory conditions. After testing several scenarios, the situation can be mitigated by limiting the value set in shost->nr_hw_queues to 4. Although the shost values were changed, the driver still had per-cpu hardware queues of its own that allowed parallelization per-cpu. Testing revealed that even with the smallish number for nr_hw_queues for SCSI-MQ, performance levels remained near maximum with the within-driver affiinitization. A module parameter was created to allow the value set for the nr_hw_queues to be tunable. Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com> Signed-off-by: James Smart <jsmart2021@gmail.com> Reviewed-by: Ming Lei <ming.lei@redhat.com> Reviewed-by: Ewan D. Milne <emilne@redhat.com> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.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.