Re: decaying average for %CPU

[Nick Piggin <piggin@cyberone.com.au>]

Albert Cahalan wrote:

>On Thu, 2003-10-16 at 22:56, Nick Piggin wrote:
>
>>Albert Cahalan wrote:
>>
>>
>>>The UNIX standard requires that Linux provide
>>>some measure of a process's "recent" CPU usage.
>>>Right now, it isn't provided. You might run a
>>>CPU hog for a year, stop it ("kill -STOP 42")
>>>for a few hours, and see that "ps" is still
>>>reporting 99.9% CPU usage. This is because the
>>>kernel does not provide a decaying average.
>>>
>>I think the kernel provides enough info for userspace to do
>>the job, doesn't it?
>>
>
>I'm pretty sure not. Linux provides:
>
>per-process start time
>current time
>per-process total (lifetime) CPU usage
>units of time measurement (awkwardly)
>boot time
>

But your userspace program can calculate deltas in the total
CPU statistics. Yep, its in /proc/stat.

>
>>From that you can compute %CPU over the whole
>life of the process. This does not meet the
>requirements of the UNIX standard.
>
>What we do for load average is about right,
>except that per-process values can't all get
>updated at the same time. So the algorithm
>needs to be adjusted a bit to allow for that
>

load average is not CPU load though