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If AMD Performance Monitoring Version 2 (PerfMonV2) is supported, use a new scheme to process Core PMC overflows in the NMI handler using the new global control and status registers. This will be bypassed on unsupported hardware (x86_pmu.version < 2). In x86_pmu_handle_irq(), overflows are detected by testing the contents of the PERF_CTR register for each active PMC in a loop. The new scheme instead inspects the overflow bits of the global status register. The Performance Counter Global Status (PerfCntrGlobalStatus) register has overflow (PerfCntrOvfl) bits for each PMC. This is, however, a read-only MSR. To acknowledge that overflows have been processed, the NMI handler must clear the bits by writing to the PerfCntrGlobalStatusClr register. In x86_pmu_handle_irq(), PMCs counting the same event that are started and stopped at the same time record slightly different counts due to delays in between reads from the PERF_CTR registers. This is fixed by stopping and starting the PMCs at the same before and with a single write to the Performance Counter Global Control (PerfCntrGlobalCtl) upon entering and before exiting the NMI handler. Signed-off-by: Sandipan Das <sandipan.das@amd.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/f20b7e4da0b0a83bdbe05857f354146623bc63ab.1650515382.git.sandipan.das@amd.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.