2b0569b3b7
Introduce the module parameter 'use_msi' which, when set, uses MSI interrupts instead of doorbells for each queue pair (QP). The parameter is only available if NTB MSI support is configured into the kernel. We also require there to be more than one memory window (MW) so that an extra one is available to forward the APIC region. To use MSIs, we request one interrupt per QP and forward the MSI address and data to the peer using scratch pad registers (SPADS) above the MW SPADS. (If there are not enough SPADS the MSI interrupt will not be used.) Once registered, we simply use ntb_msi_peer_trigger and the receiving ISR simply queues up the rxc_db_work for the queue. This addition can significantly improve performance of ntb_transport. In a simple, untuned, apples-to-apples comparision using ntb_netdev and iperf with switchtec hardware, I see 3.88Gb/s without MSI interrupts and 14.1Gb/s wit MSI, which is a more than 3x improvement. Signed-off-by: Logan Gunthorpe <logang@deltatee.com> Cc: Dave Jiang <dave.jiang@intel.com> Cc: Allen Hubbe <allenbh@gmail.com> Signed-off-by: Jon Mason <jdmason@kudzu.us>
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.