3 Replies Latest reply on May 24, 2013 9:02 AM by Abdel Rahman Farag Hegazi

    Weird phenomenon about power of SCC chip: more cores booted, less power comsumption

    dagger

      Hi All,

       

      When using Barrelfish installed on SCC, I found a weird phenomenon that, the more number of cores which I boot Barrelfish on, the less power (exactly the current, the voltage do not change) whole chip  consumes. What's more, the decrease of current for each booted core is nearly the same. This is different with my normal ideas, and makes me confused.

       

      Can anybody explain this phenomenon?

       

      Some explaination of the experiment:

      1. The menu.lst used to boot Barrelfish contains no application which utilizes DVFS mechanism

      2. I used "sccBmc -c status" on MCPC to monitor the power of the SCC chip, and read the "3V3SCC:" item as voltage and current of the SCC chip.

      3. Following table is the decrease of current when different # of cores Barrelfish booted on (voltage keeps at 3.3V):

       

      booted core #current after booteddecreased currentdecreased current per core
      015.24800.0000
      414.75200.49600.1240
      814.25700.99100.1239
      2412.27702.97100.1238
      3211.38603.86200.1207
      489.50505.74300.1196

       

      Thanks,

      Zhiquan

        • 1. Re: Weird phenomenon about power of SCC chip: more cores booted, less power comsumption
          andrea.bartolini

          I am sorry if I am imprecised, but I am not an expert of the boot sequence of the SCC cores. But if I am not remembering wrong, a core not booted up in SCC is some how polling for a first istruction to execute, and this is a sort of busy waiting. One a kernel image is loaded in it does not perform anymore this operation and the power in idle is lower.

          You should check if by executing a power virus on the active core is leading to an higher power consumpton than the not booted core state. This should clarify that the power in not booted state is anyway below the maximum power consumption.

           

          You should also double checked if the single voltage islands preserve the same value while you are booting up an increased number of cores.

           

          Best,

          Andrea

          • 2. Re: Weird phenomenon about power of SCC chip: more cores booted, less power comsumption
            dagger

            But if I am not remembering wrong, a core not booted up in SCC is some how polling for a first istruction to execute, and this is a sort of busy waiting. One a kernel image is loaded in it does not perform anymore this operation and the power in idle is lower.

            Thanks a lot for your answer, Andrea.

             

            I still have another question about the power model of the chip.

            They said the dynamic power is proportional to the product of frequency and squared voltage. I thought the power of the chip under certain V/F setting is constant whether what program runs on the chip.

            But actually the power of the chip is related to the program running on the chip. For example, the idle power is lower than non-idle power. memory-bound power is lower than compute-bound power, and as you said, busy waiting power is lower than  maximum power consumption...

             

            So, my question is, what is the real power model of the chip ? Is the power related to program profile (cpu-boundness, or # of instructions per second, etc) ?

             

            Thanks,

            Zhiquan

            • 3. Re: Weird phenomenon about power of SCC chip: more cores booted, less power comsumption
              Abdel Rahman Farag Hegazi

              Hello Ziquan, Andrea

              I actually have a question regarding your question, when running Barrelfish on SCC and if you want to boot a new core later after you already have set of running core, does that mean that you need to reboot the whole chip to start the new one with the other running or there is a whatever command let us to start and boot this specific core while the others are running, briefly how to boot w new core without rebooting the whole running currently?

               

              Hegazi