Re: [RFC][PATCH v2 5/7] taskstats: Improve cumulative CPU timeaccounting

[Martin Schwidefsky]

On Mon, 15 Nov 2010 19:10:06 +0100
Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote:

> On Mon, 2010-11-15 at 19:00 +0100, Martin Schwidefsky wrote:
> > On Mon, 15 Nov 2010 18:51:57 +0100
> > Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote:
> > 
> > > On Mon, 2010-11-15 at 18:49 +0100, Martin Schwidefsky wrote:
> > > > > To what purpose? 
> > > >  
> > > > Is that a trick question? Why do we have tools like "top"? Or process
> > > > accounting? The point is that the quality of the numbers we get right
> > > > now is rather bad, the overhead of scanning /proc is horrendous and
> > > > the 10ms granularity is rather coarse. 
> > > 
> > > But you're not just replacing top, you're adding all kinds of new
> > > accounting crap all over the place.
> > 
> > We DO replace top. Patch #7 of 7.
> 
> You _also_ replace top, but its not by far the only thing you do. If you
> simply replaced top you wouldn't need to add tons of extra accounting,
> would you?

There are basically two things we want to accomplish:
1) Make top faster by replacing the /proc based data gathering with taskstats.
   To really make it go fast with taskstats we filter with last_depart to
   read only tasks that have changed since the last snapshot.
2) Make top more precise. That is where all of the extra accounting comes
   into play.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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