Re: Incorrect CPU process accounting using CONFIG_HZ=100

[Con Kolivas <kernel@kolivas.org>]

Peter Williams writes:

> Al Boldi wrote:
> > Peter Williams wrote:

> > twice:
> > 	1. for external proc monitoring, using a probed approach
> > 	2. for scheduling, using an inlined approach
>
> Not exactly (e.g. there's no separation between user and sys time 
> available in line) but the possibilities are there.
>
> > Wouldn't merging the two approaches be in the interest of conserving cpu 
> > resources, while at the same time reflecting an accurate view of cpu 
> > utilization?
>
> I think that this would be a worthwhile endeavour once/if sched_clock() 
> is fixed.  This is especially the case as CPUs get faster as many tasks 
> may run to completion in less than a tick.

That may not be as simple as it seems. To properly account system v user 
time using the sched_clock we'd have to hook into arch dependant asm code to 
know when entering and exiting kernel context. That is far more invasive 
than the simple on/off runqueue timing we currently do for scheduling 
accounting.

--
-ck

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