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

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  • 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...

    http://www.phoronix.com/scan.php?pag...x-4.14-AMD-CPB

  • #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

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    • #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

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      • #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.

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        • #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)

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          • #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".

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

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

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                • #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.

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                  • #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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