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List:       busybox
Subject:    Re: busybox top and multiple cpu cores
From:       Denys Vlasenko <vda.linux () googlemail ! com>
Date:       2016-10-07 17:10:42
Message-ID: CAK1hOcMMx_Ws6Ns9QvDAU0Exwy0VfXouynicbHE83679CP7O6w () mail ! gmail ! com
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On Thu, Oct 6, 2016 at 12:46 PM, Yan Seiner <yan@seiner.com> wrote:
> How does busybox handle multiple cpu cores?
>
> The 'standard' top will show multiples of 100%, so a 4 core hyperthreaded
> cpu can go to 800% utilization.
>
> Busybox seems to cap at 100%.  I have a dual core cpu, and I'm not seeing
> utilization above 100%.  As the one process I have is single-threaded, I'm
> confused as to what's happening.  A single process on a dual core machine
> should take 100% in which case other processes could use the "other" 100%,
> or if it is normalized to 100% for all cores, it should not take more than
> 50%.

Yes. A different convention.

The convention that single task does not ever use >100% CPU
(IOW: that 100% means "all CPUs were running this task thereads all the time
since last update) helps with output formatting: %CPU column can be
only 4 chars wide and it's always enough, even one digit after decimal
point fits there. Examples: " 0.0", "54.0", " 100" (needs no decimal point).

If %CPU would be allowed to go up to NCPUS*100, on machines with more than 9
CPUs you need a wider column. With more than 99 CPUs, add one more char.

Knights Landing single-socket machines today have 288 CPUs.
[well, actually 304, if all 38 tiles are functional, but Intel doesn't sell
such CPUs as of now - always disables at least 2 tiles]
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