Linux 4.14 Ensures The "Core Performance Boost" Bit Gets Set For AMD Ryzen CPUs

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  • phoronix
    Administrator
    • Jan 2007
    • 67364

    Linux 4.14 Ensures The "Core Performance Boost" Bit Gets Set For AMD Ryzen CPUs

    Phoronix: Linux 4.14 Ensures The "Core Performance Boost" Bit Gets Set For AMD Ryzen CPUs

    Recently making waves in our forums was talk of a kernel patch to address a case where the AMD CPB (Core Performance Boost) isn't being exposed by Ryzen processors. Here's more details on that and some benchmarks...

    Phoronix, Linux Hardware Reviews, Linux hardware benchmarks, Linux server benchmarks, Linux benchmarking, Desktop Linux, Linux performance, Open Source graphics, Linux How To, Ubuntu benchmarks, Ubuntu hardware, Phoronix Test Suite
  • tildearrow
    Senior Member
    • Nov 2016
    • 7097

    #2
    Minor typo?

    Originally posted by phoronix View Post
    and indicated from /proc/cpu via the flags line
    (it's /proc/cpuinfo)
    Last edited by tildearrow; 17 October 2017, 04:15 PM. Reason: meant to use a question mark

    Comment

    • FireBurn
      Senior Member
      • Dec 2007
      • 2127

      #3
      I thought boost was used when the CPU was cool enough, how does this work for Ryzen when the thermal driver doesn't land until 4.15

      Comment

      • Zan Lynx
        Senior Member
        • Jan 2012
        • 901

        #4
        Originally posted by FireBurn View Post
        I thought boost was used when the CPU was cool enough, how does this work for Ryzen when the thermal driver doesn't land until 4.15
        The CPU knows its own internal temperature. AFAIK, XFR does not require anything from the OS. It just does its thing.

        Comment

        • monte84
          Phoronix Member
          • Mar 2009
          • 64

          #5
          I don't think CPB works with the performance CPU governor. When I enable the performance governor, all CPU cores at locked at their base frequency. I have watched through (watch grep "cpu MHz" /proc/cpuinfo)

          Comment

          • dwagner
            Senior Member
            • Aug 2017
            • 392

            #6
            Just start a single-threaded CPU eating process and watch the output of "turbostat" while it runs - I can see frequencies above the base clock being used, automatically, even though /proc/cpuinfo does not indicate "cpb".

            Comment

            • Kendji
              Senior Member
              • Dec 2015
              • 222

              #7
              There's virtually no or very little performance difference.

              Comment

              • soulsource
                Senior Member
                • Aug 2014
                • 215

                #8
                /proc/cpuinfo does not display turbo frequencies. If you want to see those, you'll need another tool, like cpupower.

                Comment

                • sdack
                  Senior Member
                  • Mar 2011
                  • 1728

                  #9
                  Originally posted by Kendji View Post
                  There's virtually no or very little performance difference.
                  For a change as small as this to result in a gain of 1%-5% and for all Ryzen CPUs is actually huge, and I dare say it's exciting to see.

                  Since this went into 4.14 already has 4.15 now been deprived of further excitements.

                  Comment

                  • mlau
                    Senior Member
                    • Sep 2006
                    • 778

                    #10
                    Originally posted by Kendji View Post
                    There's virtually no or very little performance difference.
                    It only works when you tax only a single core, and the rest are ideally below the rated frequency. For example, use the ondemand governor, start e.g. scimark
                    and then do 'cat /sys/devices/system/cpu/cpufreq/policy*/scaling_cur_freq' in a terminal repeatedly. You'll see one core and its HT sibling go beyond the rated speed.
                    I've seen my 1800X go up to 4.0GHz in some very rare instances, but it never hit 4.1, and realistically goes between 3.7 and 3.9 GHz when 2 or more cores are busy.

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