Re: [patch] sched: accurate user accounting

[Con Kolivas <kernel@kolivas.org>]

On Sunday 25 March 2007 21:34, malc wrote:
> On Sun, 25 Mar 2007, Ingo Molnar wrote:
> > * Con Kolivas <kernel@kolivas.org> wrote:
> >> For an rsdl 0.33 patched kernel. Comments? Overhead worth it?
> >
> > we want to do this - and we should do this to the vanilla scheduler
> > first and check the results. I've back-merged the patch to before RSDL
> > and have tested it - find the patch below. Vale, could you try this
> > patch against a 2.6.21-rc4-ish kernel and re-test your testcase?
>
> [..snip..]
>
> Compilation failed with:
> kernel/built-in.o(.sched.text+0x564): more undefined references to
> `__udivdi3' follow
>
> $ gcc --version | head -1
> gcc (GCC) 3.4.6
>
> $ cat /proc/cpuinfo | grep cpu
> cpu             : 7447A, altivec supported
>
> Can't say i really understand why 64bit arithmetics suddenly became an
> issue here.

Probably due to use of:

#define NS_TO_JIFFIES(TIME)	((TIME) / (1000000000 / HZ))
#define JIFFIES_TO_NS(TIME)	((TIME) * (1000000000 / HZ))

Excuse our 64bit world while we strive to correct our 32bit blindness and fix 
this bug.

>
> Am i supposed to run the testcase and see if numbers in `/proc/stat'
> now match the reality closer? To be really accurate `/proc/stat'
> should be left alone methinks, because no matter how good you try the
> fundamential fact that time(and consequently load percentage) is not
> really devided in USER_HZ intervals will interfere with ones quest for
> accurate statistics. (Wonder what this patch will do to slightly modified
> hog that produced this: http://www.boblycat.org/~malc/apc/load-c2d-hog.png
> but this will have to wait till i get to the PC at work)

It should far more accurately represent the cpu usage without any userspace 
changes.

-- 
-ck