eb3693f052
The scaling factor between HWP performance levels and CPU frequency may be different for different types of CPUs in a hybrid processor and in general the HWP performance levels need not correspond to "P-states" representing values that would be written to MSR_IA32_PERF_CTL if HWP was disabled. However, the policy limits control in cpufreq is defined in terms of CPU frequency, so it is necessary to map the frequency limits set through that interface to HWP performance levels with reasonable accuracy and the behavior of that interface on hybrid processors has to be compatible with its behavior on non-hybrid ones. To address this problem, use the observations that (1) on hybrid processors the sysfs interface can operate by mapping frequency to "P-states" and translating those "P-states" to specific HWP performance levels of the given CPU and (2) the scaling factor between the MSR_IA32_PERF_CTL "P-states" and CPU frequency can be regarded as a known value. Moreover, the mapping between the HWP performance levels and CPU frequency can be assumed to be linear and such that HWP performance level 0 correspond to the frequency value of 0, so it is only necessary to know the frequency corresponding to one specific HWP performance level to compute the scaling factor applicable to all of them. One possibility is to take the nominal performance value from CPPC, if available, and use cpu_khz as the corresponding frequency. If the CPPC capabilities interface is not there or the nominal performance value provided by it is out of range, though, something else needs to be done. Namely, the guaranteed performance level either from CPPC or from MSR_HWP_CAPABILITIES can be used instead, but the corresponding frequency needs to be determined. That can be done by computing the product of the (known) scaling factor between the MSR_IA32_PERF_CTL P-states and CPU frequency (the PERF_CTL scaling factor) and the P-state value referred to as the "TDP ratio". If the HWP-to-frequency scaling factor value obtained in one of the ways above turns out to be euqal to the PERF_CTL scaling factor, it can be assumed that the number of HWP performance levels is equal to the number of P-states and the given CPU can be handled as though this was not a hybrid processor. Otherwise, one more adjustment may still need to be made, because the HWP-to-frequency scaling factor computed so far may not be accurate enough (e.g. because the CPPC information does not match the exact behavior of the processor). Specifically, in that case the frequency corresponding to the highest HWP performance value from MSR_HWP_CAPABILITIES (computed as the product of that value and the HWP-to-frequency scaling factor) cannot exceed the frequency that corresponds to the maximum 1-core turbo P-state value from MSR_TURBO_RATIO_LIMIT (computed as the procuct of that value and the PERF_CTL scaling factor) and the HWP-to-frequency scaling factor may need to be adjusted accordingly. Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> |
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| LICENSES | ||
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
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| COPYING | ||
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| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
README
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.