times()

times()

[João Fernandes Simplício]

Hello,

I've been testing the times() function and I can't understand in what
way is the ticking being incremented for system time measurement
(tms_stime). I understand that tms_utime gives the ticking related to
the process and what does tms_stime gives?

E.g.:

In 5 minutes the process gives 10000 ticks, so if the OS supports a
maximum of 32758 process identifiers this gives us a 30% of load.

Is my thinking right or am I missing something else?

Best Regards,

     -- João Simplício
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Re: times()

[Glynn Clements]

João Fernandes Simplício wrote:

> I've been testing the times() function and I can't understand in what
> way is the ticking being incremented for system time measurement
> (tms_stime). I understand that tms_utime gives the ticking related to
> the process and what does tms_stime gives?

tms_utime is the amount of CPU time spent executing user-space code
(i.e. the executable and shared libraries), while tms_stime is the
amount of CPU time spent in the kernel.

> E.g.:
> 
> In 5 minutes the process gives 10000 ticks, so if the OS supports a
> maximum of 32758 process identifiers this gives us a 30% of load.
> 
> Is my thinking right or am I missing something else?

The number of PIDs doesn't come into it.

times() reports the CPU time used by a single process.

If sysconf(_SC_CLK_TCK) is 100, then 5 minutes is 5*60*100 = 30000
ticks, so 10000 ticks corresponds to 33% of the CPU time being used by
that process.

Also, note that 100% correponds to full utilisation of a single CPU. 
If you have multiple CPUs (a single CPU chip with multiple cores is
treated as multiple CPUs), a multi-threaded process can exceed 100%
CPU.

-- 
Glynn Clements <glynn@gclements.plus.com>
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