powerd and increase in energy need

[Olivier Smedts]

2012/3/21 Kevin Oberman <kob6558 at gmail.com>:
> If you are trying to reduce power consumption, why are you limiting Cx
> states to C2 (which save little) and not C3 (which will save a LOT of
> power when the CPU is not heavily loaded).

Jumping up on this but I don't know if that's related to his reasons
to not use C3. Mine are simple :
# sysctl dev.cpu | grep temperature
dev.cpu.0.temperature: 39,0C
dev.cpu.1.temperature: 40,0C
dev.cpu.2.temperature: 36,0C
dev.cpu.3.temperature: 36,0C
dev.cpu.4.temperature: 41,0C
dev.cpu.5.temperature: 41,0C
dev.cpu.6.temperature: 36,0C
dev.cpu.7.temperature: 36,0C
# sysctl hw.acpi.cpu.cx_lowest=C3
hw.acpi.cpu.cx_lowest: C2 -> C3
# sysctl dev.cpu | grep temperature
dev.cpu.0.temperature: 44,0C
dev.cpu.1.temperature: 44,0C
dev.cpu.2.temperature: 40,0C
dev.cpu.3.temperature: 40,0C
dev.cpu.4.temperature: 46,0C
dev.cpu.5.temperature: 46,0C
dev.cpu.6.temperature: 41,0C
dev.cpu.7.temperature: 41,0C
# sysctl hw.acpi.cpu.cx_lowest=C2
hw.acpi.cpu.cx_lowest: C3 -> C2
# sysctl dev.cpu | grep temperature
dev.cpu.0.temperature: 40,0C
dev.cpu.1.temperature: 40,0C
dev.cpu.2.temperature: 36,0C
dev.cpu.3.temperature: 36,0C
dev.cpu.4.temperature: 42,0C
dev.cpu.5.temperature: 42,0C
dev.cpu.6.temperature: 36,0C
dev.cpu.7.temperature: 36,0C

Only 1-2 seconds between each command, no current load. As you can
see, when I engage C3 states, the CPU temperature increases by 4-5°C.
I expected it to drop.

This is with :
# sysctl dev.cpu | grep freq
dev.cpu.0.freq: 2933
dev.cpu.0.freq_levels: 2933/95 2799/95 2266/75 1733/56 1199/39
# grep perf /etc/rc.conf
performance_cx_lowest="C2"
performance_cpu_freq="HIGH"
# grep hint /boot/loader.conf
hint.p4tcc.0.disabled=1
hint.acpi_throttle.0.disabled=1
# dmesg | head -n 13 | tail -n 9
FreeBSD 9.0-STABLE #0 r233000M: Thu Mar 15 12:30:27 CET 2012
    root at zozo.afpicl.lan:/usr/obj/usr/src/sys/CORE amd64
CPU: Intel(R) Core(TM) i7 CPU         860  @ 2.80GHz (2793.04-MHz K8-class CPU)
  Origin = "GenuineIntel"  Id = 0x106e5  Family = 6  Model = 1e  Stepping = 5
  Features=0xbfebfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,DTS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE>
  Features2=0x98e3fd<SSE3,DTES64,MON,DS_CPL,VMX,SMX,EST,TM2,SSSE3,CX16,xTPR,PDCM,SSE4.1,SSE4.2,POPCNT>
  AMD Features=0x28100800<SYSCALL,NX,RDTSCP,LM>
  AMD Features2=0x1<LAHF>
  TSC: P-state invariant, performance statistics

I tried with and without powerd and there's no noticeable difference,
so I don't use it. I also tried with and without
performance_cpu_freq="HIGH" in /etc/rc.conf (without, dev.cpu.0.freq
is 2799 so I don't think TurboBoost is enabled in this case).

> If it is due to the system hanging, it is almost certainly because you
> have throttling enabled. Throttling, either by the use of TCC (also
> called P4TCC) or the older, externally implemented throttling
> mechanism, is a BAD BAD THING! I have complained for years about it
> being the default. It is intended for thermal control, not power
> management. The power savings will be negligible and, in combination
> with deep sleep modes (Cx > 2) can and do result in the CPU going into
> deep sleep and never waking up.
>
> You can (and should) disable them in /boot/loader.conf with:
> # Disable CPU throttling
> hint.p4tcc.0.disabled=1
> hint.acpi_throttle.0.disabled=1
>
> This should greatly reduce the large number of "frequencies"
> available, but they will be the ones provided by EST.which really do
> reduce power consumption. (I put frequencies in quotation marks
> because throttling does not really change the clock speed. It simply
> skips 'N' of every 8 clock cycles. Still, compared to C3 and higher,
> EST is a minor power savings.
>
> Just following the recommendations on the power management web page is
> the way to go.
> --
> R. Kevin Oberman, Network Engineer
> E-mail: kob6558 at gmail.com
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-- 
Olivier Smedts                                                 _
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