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It was observed that some of the high performance benchmarks are spending more time in kernel depending on which CPU package they are executing. The difference is significant and benchmark scores varies more than 10%. These benchmarks adjust class of service to improve thread performance which run in parallel. This class of service change causes access to MMIO region of Intel Speed Select PCI devices depending on the CPU package they are executing. This mapping from CPU to PCI device instance uses a standard Linux PCI interface "pci_get_domain_bus_and_slot()". This function does a linear search to get to a PCI device. Since these platforms have 100+ PCI devices, this search can be expensive in fast path for benchmarks. Since the device and function of PCI device is fixed for Intel Speed Select PCI devices, the CPU to PCI device information can be cached at the same time when bus number for the CPU is read. In this way during runtime the cached information can be used. This improves performance of these benchmarks significantly. Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> Link: https://lore.kernel.org/r/20210616221329.1909276-1-srinivas.pandruvada@linux.intel.com Reviewed-by: Hans de Goede <hdegoede@redhat.com> Signed-off-by: Hans de Goede <hdegoede@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.