5 Replies Latest reply on Jun 21, 2013 1:14 PM by sylvia_intel

    DVFS capabilities in latest Intel processors

    KARTHIK

      Hi,

      I would like to know whether we can change the frequency of the intel multi-core processors individually. I have Intel Core2Duo CPU T5750 which has 2 cores. When I run cpufreq-info in Linux I get to know that both the cores will run in the same hardware frequency. Please find cpufreq-info output below(Relevant data shown)

      $ cpufreq-info
      *******************
      analyzing CPU 0:
      driver: acpi-cpufreq
      CPUs which run at the same hardware frequency: 0 1
      CPUs which need to have their frequency coordinated by software: 0
      maximum transition latency: 10.0 us.
      hardware limits: 1000 MHz - 2.00 GHz
      available frequency steps: 2.00 GHz, 1.67 GHz, 1.33 GHz, 1000 MHz
      ********************

      ********************
      analyzing CPU 1:
      driver: acpi-cpufreq
      CPUs which run at the same hardware frequency: 0 1
      CPUs which need to have their frequency coordinated by software: 1
      maximum transition latency: 10.0 us.
      hardware limits: 1000 MHz - 2.00 GHz
      available frequency steps: 2.00 GHz, 1.67 GHz, 1.33 GHz, 1000 MHz

      Hence by above output I expect both cores to vary its frequency in a synchronous fashion.

      But when I tried to check the frequency of each core by using the information in /proc/cpuinfo, I see that the cores are varying its frequency individually. The command I used and its output are below:

      $ while true; do grep -e "cpu MHz" /proc/cpuinfo; echo "===";sleep 0.1; done

      cpu MHz : 1000.000
      cpu MHz : 1000.000
      ===
      cpu MHz : 2000.000
      cpu MHz : 1000.000
      ===
      cpu MHz : 1000.000
      cpu MHz : 1000.000
      ===
      cpu MHz : 1000.000
      cpu MHz : 1000.000
      ===
      cpu MHz : 1000.000
      cpu MHz : 2000.000
      ===
      cpu MHz : 1000.000
      cpu MHz : 1000.000
      ===
      ******************

      ******************

      Hence my questions are:

      1) Can someone explain why the cores change the frequency individually even though the cpurfreq-info says that both the cores run at the same hardware frequency? Am I missing something?

      2) Does latest intel multi-core chips have per-core DVFS? Kindly let me know.

      3) Can voltage and frequency can be changed independent of each other in latest multicore processors using EIST (Enhanced Intel Speed Step Technology)?

      Kindly let me know your comments...

      Thanks for your time,

      Karthik.V.M.

      Note:

      The cpu frequency can be more neatly obtained using the following command:

      $ watch -n 0.1 grep \"cpu MHz\" /proc/cpuinfo


        • 1. Re: DVFS capabilities in latest Intel processors
          Freddy Gonzalez

          Do you have Enhanced Intel SpeedStep® Technology enabled in the BIOS?  What it does is allows the system to dynamically adjust processor voltage and core frequency, which can result in decreased average power consumption and decreased average heat production.

           

          In case you disable this feature, the processor will be always running at the max speed 2.0GHZ even in idle mode.

           

          Regards,

          1 of 1 people found this helpful
          • 2. Re: DVFS capabilities in latest Intel processors
            KARTHIK

            Hi Freddy,

             

            Thanks a lot for your response. I was tied up a bit so could not reply immediately.

             

            Actually Enhanced Intel Speed Step Technology is working well in my laptop. I see that cores increase or decrease the frequency based on processor load. But my question is that as cpufreq-info data(in my previous post) says that both core1 and core2 run at the same hardware frequency I expected both cores to always be in the same frequency. But when you see the output of the "while" command in my previous post you can clearly see that both cores run at different frequency. It seems as if both cores can independently vary their frequency for handling the load. This is contradictory to cpufreq-info data. That is why I got confused. Any clarification on this point is more appreciated.

             

            Regards,

            karthik

            • 3. Re: DVFS capabilities in latest Intel processors
              sylvia_intel

              Karthik,

               

              What we can say and confirm is that Intel® Multicore processors have the capability to automatically adjust the Core voltage and speed individually and this is possible due to the new technologies included with them like Intel® Turbo Boost Technology, Intel® Enhanced Speed Stepping Technology and the different C states. It is expected to see the CPU cores showing different clock frequencies depending on the work flow.

               

              Regards.

              • 4. Re: DVFS capabilities in latest Intel processors
                KARTHIK

                Hi Sylvia,

                 

                Thanks for your prompt reply. My main intent of asking the question is to know whether cores in the latest intel multi-core chip can vary their frequencies individually. Based on a bit of research I finally came to know that as you have mentioned above the processor can vary core voltage and frequency to save power(Intel Enhanced Speed Step) and for improving performance(Turbo Boost). But I came to know that the voltage and frequency of all the cores of the latest intel multi-core processor will be changed simultaneously. It is not that each core can run in different frequency.

                 

                My initial outputs(while loop command line) show that each core is varying its frequency individually. That is actually due to the OS requesting individual frequency for different cores. The output only represent what frequency the OS has requested for a core. But the hardware in the Intel Multi-core processor accepts these OS requests for different cores and then sets the frequency of all the cores to the best value to save power or improve performance. Hence finally all cores run in the same frequency though OS requests different values. Please feel free to correct me.

                 

                Regards,

                karthik

                • 5. Re: DVFS capabilities in latest Intel processors
                  sylvia_intel

                  Karthik, 
                  It is an expected behavior all cores runs a different speed, as I explained you on the previous post. The processor has the ability, by design, to adjust the speed and the voltage.

                   

                  Regarding the information you are getting I’m afraid we do not know, so I recommend you to contact a Linux developer, to understand how this command suppose to work.

                  It could be that the first command reads the initial speed of all cores and then, the output command reads the speed they are actually running.


                  Regards.