Re: decaying average for %CPU

[Nick Piggin]

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.


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