Re: CPU Access in the Kernel

Stephen Morris <samorris@xxxxxxxxxxxxxxx> · Thu, 30 Jun 2022 09:22:49 +1000



    On 29/6/22 21:29, George N. White III wrote:

    
        On Wed, Jun 29, 2022 at 5:43 AM Stephen Morris
          <samorris@xxxxxxxxxxxxxx>
          wrote:

        
          On 22/6/22 23:54, Matthew
            Miller wrote:

            > [...] 

          
            > Or, `cpu-x` for a GUI view with a lot of detail.

            Thanks Greg. I installed cpu-x and tried all the commands.
            What makes 

            the first two processes difficult from my perspective is the
            cpu I have 

            has 32 treads all of which are the same so the first two
            processes lists 

            all 32.

            I ran the cpu-x bench marks for random numbers and what was
            interesting 

            was the results for 32 threads were only around 16 times the
            result for 

            1 thread, which is probably to be expected given the cpu has
            16 cores.

          
          My experience was that disabling hyperthreading didn't
            reduce throughput.

          
          These multi-core systems generally do better with integer
            workloads, I think some
          have one f.p. unit per core.   There can be very
            counterintuitive performance 

          
          changes due to CPU cache issues and communications
            overhead.  My experience
          is mostly with I/O intensive workloads.  We generally
            found it best to limit those tasks 

          
          to a fraction of the cores so background tasks (job
            control/monitoring, backups, etc) 

          
          didn't stall.  After a big effort to make efficient use
            of all the cores you may 

          
          encounter thermal throttling.   It was better to adjust
            the workload to avoid 

          
          thermal issues: more consistent thruput and fewer issues
            with background tasks. 

          
    Thanks George, I have experienced the same things myself. Having
    installed cpu-x for the first time I was just trying it out, and it
    default benchmark mode was 1 minute and 1 thread with slow random
    number generation and fast random number generation, I haven't done
    any investigation to determine exactly what that means. So a ran a
    test on the default setting, then ran a test on 32 threads which
    returned a result that was around 16 times the results from a single
    thread. Which I was not surprised at as being a 16 core dual channel
    cpu, and hence Windows and Fedora consider it to have 32 logical
    cores, it doesn't matter how many channel are available for each
    core the total throughput is only what a core is capable of
    producing.

    
    regards,

    Steve

    
          -- 

        
            George N. White III

              
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