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Nailing Down The Linux Kernel Power Regressions

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  • #11
    Originally posted by not.sure View Post
    This dude claims that he can read out cheap power meters on his ubuntu server:
    http://www.linux-depot.com/?p=projects&s=powermeter
    http://www.eco-eye.com/products.html
    This is a possible solution but this kind of power meter measure only the current through an Hall sensor from what I can see(Eco-eye Elite 200). I think you put manually the voltage hence any voltage variation will not be taking in account.
    Ex: Nominal voltage is 230V an you read a consumption of 1A so the power is 230W but if the delivered voltage is only 220V (a +- 10% variation is totally normal) you will consume 220W but the reading will still be 230W. I think it's not good enough to make tests.

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    • #12
      Originally posted by glasen View Post
      Just my idea:

      Point a web-cam to this device, do a little OCR magic and you have your numbers.
      Too much work with too little ROI.
      Michael Larabel
      http://www.michaellarabel.com/

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      • #13
        Originally posted by frederir View Post
        Hi,

        In order to measure power consumption I'd suggest to use multimeters instead of an UPS. The precision of the UPS is not known and it can change greatly from a manufacturer to another leading to unreproducible results.

        A bit over your budget ($140 to $150) but a better solution would be to use two VA18B DMM with usb interface, one to measure voltage, the other to measure current and then combine the two to have power.

        At http://www.multimeterwarehouse.com/VA18B.htm the VA18 is $70 and at http://multimeter.schewe.com/ you can get a software to read data from usb.

        It involves a little "surgery" on the power chord in order to measure the current (you must cut one cable and attach 2 banana plugs to put the amper-meter serially) but the measures will be better then with a reading from a UPS.

        If needed I can provide a more detailed schematic.
        Too much work with too little ROI.
        Michael Larabel
        http://www.michaellarabel.com/

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        • #14
          Voltcraft?

          Originally posted by Michael View Post
          Too much work with too little ROI.
          I have a Voltcraft Energy Logger with an SD card where the data for up to ten devices can be logged. The log format needs a Windows program to be deciphered though. However there's some documentation floating around in the web that can enable you to roll your own Linux-based decoder.

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          • #15
            Originally posted by Michael View Post
            Too much work with too little ROI.
            Hardly so. The cable work is a trivial 30min job max. The meters are natively supported under Linux, it will create a tty device and you can rewrite the data-decoding perl script from the linked site to php easily. I think frederir's is a very valid solution that will also provide you with guaranteed precision, which is something you really need and probably can't get from an UPS in this price range.

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            • #16
              if you want to do ocr on lcd 7 segments there is ssocr

              http://www.unix-ag.uni-kl.de/~auerswal/ssocr/index.html

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              • #17
                Originally posted by Michael View Post
                Too much work with too little ROI.
                Well, if I was not in a remote country without reliable post-office I would set up the system and send it to you. But I disagree on the low ROI. Once you have the system up and running you can use it not only to troubleshot this particular problem, but also make measurement on the other systems and test power efficiency in your reports.
                Using DMM has the added advantage you can also use it to test DC power and isolate sub-systems (Processor power consumption from the 4pins 12V, or graphic card with external power) It would be more accurate than simply measure the total power consumption of the system.
                But thank you for the good work you are making by giving us reliable benchmark; you can only optimize what you can measure!

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                • #18
                  Originally posted by frederir View Post
                  A bit over your budget ($140 to $150) but a better solution would be to use two VA18B DMM with usb interface, one to measure voltage, the other to measure current and then combine the two to have power.
                  If you go down that path it could be worth looking for multimeters which claim to measure True RMS. Note, multiplying the readings of both multimeters will give you apparent power not real power. Might be good enough though.

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                  • #19
                    Originally posted by frief View Post
                    If you go down that path it could be worth looking for multimeters which claim to measure True RMS. Note, multiplying the readings of both multimeters will give you apparent power not real power. Might be good enough though.
                    Hum, you are totally right, without true RMS the power factor of the power supply under test will taint the results. And another consideration is the dephasage between measure of voltage and current. May be this DMM setup is not a so good idea after all ....

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                    • #20
                      with still needing to monitor them for manually toggling the AC power / battery
                      With ThinkPads and the "tp_smapi" kernel module you can discharge the battery even with AC connected by writing a "1" to "/sys/devices/platform/smapi/BAT0/force_discharge" (switching back to AC can be done by writing a 0 or automatically when the battery is empty). So your laptop won't power off when you got the AC adapter inserted and the discharging forced.

                      This way you could at least automate the "charge/build new kernel/wait until battery has reached >50%/reboot - switch to battery - measure - switch to AC" cycle with accurate (and easy!) measuring.

                      More info (with hardware compatibility matrix) is here: http://www.thinkwiki.org/wiki/Tp_smapi
                      Last edited by jannis; 06-03-2011, 08:30 AM.

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