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While the majority of server OS distributions are deployed with the "performance" governor as the default, some distributions like Ubuntu use the "powersave" governor by default. While using the "powersave" governor in its default configuration on Sapphire Rapids systems leads to much lower power, the performance is lower by more than 25% for several workloads relative to the "performance" governor. A 37% difference has been reported by www.Phoronix.com [1]. This is a consequence of using a relatively high EPP value in the default configuration of the "powersave" governor and the performance can be made much closer to the "performance" governor's level by adjusting the default EPP value. Based on experiments, with EPP of 0x00, 0x10, 0x20, the performance delta between the "powersave" governor and the "performance" one is around 12%. However, the EPP of 0x20 reduces average power by 18% with respect to the lower EPP values. [Note that raising min_perf_pct in sysfs as high as 50% in addition to adjusting EPP does not improve the performance any further.] For this reason, change the EPP value corresponding to the the default balance_performance setting for Sapphire Rapids to 0x20, which is straightforward, because analogous default EPP adjustment has been applied to Alder Lake and there is a way to set the balance_performance EPP value in intel_pstate based on the processor model already. The goal here is to limit the mean performance delta between the "powersave" governor in the default configuration and the "performance" governor for a wide variety of server workloadsto to around 10-12%. For some bursty workloads, this delta can be still large, as the frequency ramp-up will still lag when the "powersave" governor is in use irrespective of the EPP setting, because the performance governor always requests the maximum possible frequency. Link: https://www.phoronix.com/review/centos-clear-spr/6 # [1] Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> [ rjw: Subject and changelog edits ] Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> |
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| 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.