On 10/25/2013 08:13 AM, Melanie Kambadur wrote:
I appreciate you all taking the time to walk me through this. Let me
see if I understand the new comments. Intel p-states is a HW-based
power manager,
Not hardware based but specific to Intel CPUs SandyBridge+
and strictly an alternative to (i.e., it cannot be
combined with) OS governors and drivers.
Correct
If I want to use ondemand with my Dell server I need to:
Add intel_pstate=disable on your kernel commond line, this will take
intel_pstate out of the picture. For the rest of the config on the
dell system I am no help sorry.
1) Modify the BIOS to give the OS exclusive power management control
because otherwise an OS driver won't be able to work properly. (I
think I know how to do this now after some more reading, e.g. here
http://en.community.dell.com/techcenter/power-cooling/w/wiki/best-practices-in-power-management.aspx
if anyone is curious.)
2) Set the O/S cpufreq driver to acpi_cpufreq, and
3) Set the O/S cpufreq governor to ondemand.
Is that correct?
Also, which driver should I try to use if I want to test the
performance & powersave governors again (or if I replicate the
behavior of the performance governor by manually modifying the
min_perf_pct value as Dirk suggested)? Will it still be acpi_cpufreq?
If intel_pstate is being used acpi_cpufreq will not be loaded. Setting
performance with intel_pstate should work I will look to see where the
bug is.
Finally, the behavior of the C-states is totally independent of
P-states and any kind of OS-based frequency tuning policy, correct?
Correct
However, David recommends that leaving C1E on rarely hurts performance
while significantly improving power.
-Melanie
On Fri, Oct 25, 2013 at 10:40 AM, Dirk Brandewie
<dirk.brandewie@xxxxxxxxx> wrote:
On 10/24/2013 12:42 PM, Melanie Kambadur wrote:
From /sys/devices/system/cpu/cpuN/cpufreq/scaling_driver I get that
the current p-state driver is called "intel_pstate". David, you
mention that the firmware governors are not very efficient, do you
suggest replacing the intel_pstate driver with a different driver?
I will need to look and see why changing to performance isn't working
correctly.
To get the behavior of the performance governor you can use
echo 100 > /sys/devices/system/cpu/intel_pstate/min_perf_pct
This will force intel_pstate to select the highest P state and
leave it there.
Turbostat is useful for collecting frequency (P state) and idle (C state)
information.
--Dirk
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