Re: decaying average for %CPU

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

Albert Cahalan wrote:

>On Thu, 2003-10-16 at 23:21, Nick Piggin wrote:
>  
>
>>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.
>>    
>>
>
>Huh?
>
>This isn't about "top", which displays % of CPU
>time used over the refresh interval by reading
>all the process data multiple times.
>
>This is about programs like "ps", which read
>everything and then spit out the output.
>
>I hope you're not suggesting to read things
>twice with a huge sleep(5) in the middle, or
>to run some kind of daemon that polls /proc
>once a second. That's far beyond horrid.
>  
>

Yeah I spose it is.