CPU usage (Read by `top`)

[Sergey Kubushin]

On Wed, 19 Jan 2000, Richard B. Johnson wrote:

And my $0.25 - why the shared memory is always reported as 0 bytes? Is it
something mentioned somewhere in FAQs? Please give me directions if it is.

> 
> In linux 2.3.39, if the CPU is given up by calling sched_yield(), even
> though the caller may give up the CPU for many milliseconds, `top`
> still shows that the caller is using 99% of the CPU time.
> 
> This shows the problem:
> 
> 
> #include <stdio.h>
> #include <sys/time.h>
> #define MICRO 1e6
> main()
> {
>     struct timeval tv;
>     double start;
>     double stop;
>     double total;
>     for(;;)
>     {
>         gettimeofday(&tv, NULL);
>         start = ((double) tv.tv_sec * MICRO) + (double) tv.tv_usec;
>         sched_yield();
>         sched_yield();
>         sched_yield();
>         sched_yield();
>         sched_yield();
>         sched_yield();
>         sched_yield();
>         sched_yield();
>         sched_yield();
>         sched_yield();
>         gettimeofday(&tv, NULL);
>         stop = ((double) tv.tv_sec * MICRO) + (double) tv.tv_usec;
>         total = stop - start;
>         fprintf(stderr,"TT %8.2f us\n", total);
>     }
> }
> 
> Now sched_yield(), itself, works well. The problem is that the task
> that gave up the CPU is still being 'Charged' for it!
> 
> Cheers,
> Dick Johnson
> 
> Penguin : Linux version 2.3.39 on an i686 machine (800.63 BogoMips).
> 
> 
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===========================================================================
Sergey Kubushin aka the Tamer         < > The impossible we do immediately.
e-mail: ksi en ksi-linux.com  SK320-RIPE < > Miracles require 24-hour notice.
===========================================================================


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