Re: [PATCH] Staircase Scheduler v6.3 for 2.6.7-rc2

[Andrew Morton]

Phy Prabab <phyprabab@xxxxxxxxx> wrote:
>
> Also please note the degredation between
>  2.6.7-rc2-bk8-s63:
> 
>  A:  35.57user 38.18system 1:20.28elapsed 91%CPU
>  B:  35.54user 38.40system 1:19.48elapsed 93%CPU
>  C:  35.48user 38.28system 1:20.94elapsed 91%CPU
> 
>  Interesting how much more time is spent in both user
>  and kernel space between the two kernels.  Also note
>  that 2.4.x exhibits even greater delta:
> 
>  A:  28.32user 29.51system 1:01.17elapsed 93%CPU
>  B:  28.54user 29.40system 1:01.48elapsed 92%CPU
>  B:  28.23user 28.80system 1:00.21elapsed 94%CPU
> 
>  Could anyone suggest a way to understand why the
>  difference between the 2.6 kernels and the 2.4
>  kernels?

This is very very bad.

It's a uniprocessor machine, yes?

Could you describe the workload a bit more?  Is it something which others
can get their hands on?

It spends a lot of time in the kernel for a build system.  I wonder why.

At a guess I'd say either a) you're hitting some path in the kernel which
is going for a giant and bogus romp through memory, trashing CPU caches or
b) your workload really dislikes run-child-first-after-fork or c) the page
allocator is serving up pages which your access pattern dislikes or d)
something else.

It's certainly interesting.
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