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Previously, ibmvnic IRQs were assigned to CPU numbers by assigning all the IRQs for transmit queues then assigning all the IRQs for receive queues. With multi-threaded processors, in a heavy RX or TX environment, physical cores would either be overloaded or underutilized (due to the IRQ assignment algorithm). This approach is sub-optimal because IRQs for the same subprocess (RX or TX) would be bound to adjacent CPU numbers, meaning they were more likely to be contending for the same core. For example, in a system with 64 CPU's and 32 queues, the IRQs would be bound to CPU in the following pattern: IRQ type | CPU number ----------------------- TX0 | 0-1 TX1 | 2-3 <etc> RX0 | 32-33 RX1 | 34-35 <etc> Observe that in SMT-8, the first 4 tx queues would be sharing the same core. A more optimal algorithm would balance the number RX and TX IRQ's across the physical cores. Therefore, to increase performance, distribute RX and TX IRQs across cores by alternating between assigning IRQs for RX and TX queues to CPUs. With a system with 64 CPUs and 32 queues, this results in the following pattern: IRQ type | CPU number ----------------------- TX0 | 0-1 RX0 | 2-3 TX1 | 4-5 RX1 | 6-7 <etc> Observe that in SMT-8, there is equal distribution of RX and TX IRQs per core. In the above case, each core handles 2 TX and 2 RX IRQ's. Signed-off-by: Nick Child <nnac123@linux.ibm.com> Reviewed-by: Haren Myneni <haren@linux.ibm.com> Link: https://lore.kernel.org/r/20230127214358.318152-1-nnac123@linux.ibm.com Signed-off-by: Paolo Abeni <pabeni@redhat.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.