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All the fixed counters share a fixed control register. The current perf reads and re-writes the fixed control register for each fixed counter disable/enable, which is unnecessary. When changing the fixed control register, the entire PMU must be disabled via the global control register. The changing cannot be taken effect until the entire PMU is re-enabled. Only updating the fixed control register once right before the entire PMU re-enabling is enough. The read of the fixed control register is not necessary either. The value can be cached in the per CPU cpu_hw_events. Test results: Counting all the fixed counters with the perf bench sched pipe as below on a SPR machine. $perf stat -e cycles,instructions,ref-cycles,slots --no-inherit -- taskset -c 1 perf bench sched pipe The Total elapsed time reduces from 5.36s (without the patch) to 4.99s (with the patch), which is ~6.9% improvement. Signed-off-by: Kan Liang <kan.liang@linux.intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20220804140729.2951259-1-kan.liang@linux.intel.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.