Hi,
several questions, mostly about user(space) interference:
1) sysfs tunables:
- max_perf_pct, min_perf_pct
According to Documentation/cpu-freq/intel-pstate.txt this is:
max_perf_pct: limits the maximum P state that will be requested by
the driver stated as a percentage of the available performance.
min_perf_pct: limits the minimum P state that will be requested by
the driver stated as a percentage of the available performance.
Why is this needed, there already is:
scaling_max_freq, scaling_min_freq
How are both connected?
For me those tunable are doing the same and intel_pstate specific ones
should vanish to have one cpufreq min/max frequency interface exported
to userspace on all archs/cpufreq drivers.
- no_turbo: limits the driver to selecting P states below the turbo
frequency range.
Again, there is the general cpufreq "boost" tunable defined in cpufreq.c:
ssize_t show_boost(..)
static ssize_t store_boost(...)
define_one_global_rw(boost);
What is the difference, why does intel-pstate need its own tunable?
-> I'd like to integrate the intel-pstate specific stuff, mark above obsolete
and let it use the generic cpufreq tunables.
Would that work out or have I overseen something?
2) Disabling pstate driver (cpufreq in general)
There is:
intel_pstate=disable
This again is somewhat driver specific. Imo cpufreq subsystem misses a
general cpufreq.disable parameter for quite some time already.
Best would be if this works at runtime as well.
Not sure how an implementation could look like, I need to look deeper into
that, but maybe someone already has an opinion about this.
3) Why is intel-pstate needed at all?
This might have been discussed already? Would be great if someone can point
be to the discussion then.
I am interested in:
- What is the advantage over acpi-cpufreq?
- There were discussions that on modern Intel CPUs cpufreq is a kind of
obsolete power saving technique and it might be better, performance and
power wise, to disable CPU frequency alltogether and let the CPU enter
CPU idle states as quickly as possible instead.
- Are there numbers how much intel-pstate can affect performance
(theoretically in worst case and practically (specific workload?))?
Thanks,
Thomas
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