stony
Posts: 4
Joined: Sat Oct 08, 2016 5:45 pm

Pi 3 power consumption / undervolting

Sat Oct 08, 2016 6:03 pm

Hi,

got my Pi 3 yesterday and i am really happy.
(I used my Pi 1 for more then 2 years now and it works real good, but 2 nextcloud users... horror)

This is my actual config.txt at Pi 3:

Code: Select all

arm_freq=1200
arm_freq_min=150

core_freq_min=250

sdram_freq_min=250

over_voltage=-3
over_voltage_min=-8

#over_voltage_sdram_c=-3
#over_voltage_sdram_i=-3
#over_voltage_sdram_p=-3

initial_turbo=30
temp_limit=60
This is outout of vcgencmd:

Code: Select all

CPU current Frequency: frequency(45)=150000000
CORE current Frequency: frequency(1)=250000000
CPU current Temperature: temp=37.6'C
core:   	volt=1.0500V
sdram_c:	volt=1.2000V
sdram_i:	volt=1.2000V
sdram_p:	volt=1.2250V
I wonder if there is no change at sdram-voltage (does not matter what i choose -1, -2, -3, -4 ...)
Also, it seems that minimum cpu-voltage is 1.05V (= -6). I tried -7, -8, -9... but still 1.05V. Higher values are working fine.

I try to find out the min/max values for Pi 3, but i only got them for Pi 1 on elinux.org and it seems that these values are not correct (-16,8) for min/max-voltage.

If someone knows the min/max values, please let me know them :) ...or tell me what i have to do to save some energy.


Ps: yes, it is working fine as server for samba, nextcloud and squid-proxy, 90% idling at 150MHZ and 10% working hard at 1200MHZ. Actual power consumption is 2,5 Watt on idle (2,6 Watt with activated wlan driver).

Graymalk
Posts: 55
Joined: Wed Nov 11, 2015 8:33 pm

Re: Pi 3 power consumption / undervolting

Sun Oct 09, 2016 2:22 am

I... Negative values... I didn't know you could do that. :lol:

I am at the opposite end of you. I want stability so I only use positives, lol.

ejolson
Posts: 3792
Joined: Tue Mar 18, 2014 11:47 am

Re: Pi 3 power consumption / undervolting

Sun Oct 09, 2016 4:24 am

stony wrote:Hi,

got my Pi 3 yesterday and i am really happy.
(I used my Pi 1 for more then 2 years now and it works real good, but 2 nextcloud users... horror)

This is my actual config.txt at Pi 3:

Code: Select all

arm_freq=1200
arm_freq_min=150

core_freq_min=250

sdram_freq_min=250

over_voltage=-3
over_voltage_min=-8

#over_voltage_sdram_c=-3
#over_voltage_sdram_i=-3
#over_voltage_sdram_p=-3

initial_turbo=30
temp_limit=60
This is outout of vcgencmd:

Code: Select all

CPU current Frequency: frequency(45)=150000000
CORE current Frequency: frequency(1)=250000000
CPU current Temperature: temp=37.6'C
core:   	volt=1.0500V
sdram_c:	volt=1.2000V
sdram_i:	volt=1.2000V
sdram_p:	volt=1.2250V
I wonder if there is no change at sdram-voltage (does not matter what i choose -1, -2, -3, -4 ...)
Also, it seems that minimum cpu-voltage is 1.05V (= -6). I tried -7, -8, -9... but still 1.05V. Higher values are working fine.

I try to find out the min/max values for Pi 3, but i only got them for Pi 1 on elinux.org and it seems that these values are not correct (-16,8) for min/max-voltage.

If someone knows the min/max values, please let me know them :) ...or tell me what i have to do to save some energy.


Ps: yes, it is working fine as server for samba, nextcloud and squid-proxy, 90% idling at 150MHZ and 10% working hard at 1200MHZ. Actual power consumption is 2,5 Watt on idle (2,6 Watt with activated wlan driver).
Can you measure the difference in watts with stock settings? Also, I would have though you'd need arm_freq=900 or less for stability with such under volting.

stony
Posts: 4
Joined: Sat Oct 08, 2016 5:45 pm

Re: Pi 3 power consumption / undervolting

Mon Oct 10, 2016 8:29 am

Graymalk wrote:I... Negative values... I didn't know you could do that. :lol:
have a look at http://elinux.org/RPiconfig
I am at the opposite end of you. I want stability so I only use positives, lol.
Why do you use more power to get a stable system? I believe you'll get a more unstable system cause of overheating?
(My cpu is idling at ~39°C and without any changes to config.txt, it gets up to 75°C when using sysbench with 4 threads)

This is vcgencmd and full load:

Code: Select all

CPU current Frequency: frequency(45)=1200000000
CORE current Frequency: frequency(1)=400000000
CPU current Temperature: temp=51.5'C
core:   	volt=1.2375V
sdram_c:	volt=1.2000V
sdram_i:	volt=1.2000V
sdram_p:	volt=1.2250V
You see that undervolting (normal = 0 = 1.30 volt) is also available while working at high load (startet sysbench with 4 threads)
ejolson wrote:Can you measure the difference in watts with stock settings? Also, I would have though you'd need arm_freq=900 or less for stability with such under volting.
Standard settings @ 2,75 Watt idle:

Code: Select all

CPU current Frequency: frequency(45)=600000000
CORE current Frequency: frequency(1)=250000000
CPU current Temperature: temp=39.7'C
core:           volt=1.2000V
sdram_c:        volt=1.2000V
sdram_i:        volt=1.2000V
sdram_p:        volt=1.2250V
Standard settings @ 7,5 Watt full-load:

Code: Select all

CPU current Frequency: frequency(45)=1200000000
CORE current Frequency: frequency(1)=400000000
CPU current Temperature: temp=53.7'C
core:   	volt=1.3062V
sdram_c:	volt=1.2000V
sdram_i:	volt=1.2000V
sdram_p:	volt=1.2250V
Undervolting @ 2,6 Watt idle:

Code: Select all

CPU current Frequency: frequency(45)=600000000
CORE current Frequency: frequency(1)=250000000
CPU current Temperature: temp=38.6'C
core:   	volt=1.0500V
sdram_c:	volt=1.2000V
sdram_i:	volt=1.2000V
sdram_p:	volt=1.2250V
Undervolting @ 6,5 Watt full-load:

Code: Select all

CPU current Frequency: frequency(45)=1200000000
CORE current Frequency: frequency(1)=400000000
CPU current Temperature: temp=53.7'C
core:   	volt=1.2313V
sdram_c:	volt=1.2000V
sdram_i:	volt=1.2000V
sdram_p:	volt=1.2250V
Summary:
lowering MHZ saves ~0,10 Watt
lowering voltage while idling saves 0,15 Watt
lowering voltage while full-load saves 1,0 Watt
0,25€/kwH means, that i save 5,48€ / year while idling... + 10% full-load-time... should be packet cigarettes a year :mrgreen:

But back to topic... did anybody used lower (like -8 e.g.) values for undervolting successfully?

Regardes

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