Re: [Bug #11308] tbench regression on each kernel release from 2.6.22 -> 2.6.28

Linus Torvalds
2008-11-17T20:30:00Z

On Mon, 17 Nov 2008, David Miller wrote:
>
> It's on my workstation which is a much simpler 2 processor
> UltraSPARC-IIIi (1.5Ghz) system.

Ok. It could easily be something like a cache footprint issue. And while I
don't know my sparc cpu's very well, I think the Ultrasparc-IIIi is super-
scalar but does no out-of-order and speculation, no? So I could easily see
that the indirect branches in the scheduler hurt much more, and might
explain why the x86 profile looks so different.

One thing that non-NMI profiles also tend to show is "clumping", which in
turn tends to rather excessively pinpoint code sequences that release the
irq flag - just because those points show up in profiles, rather than
being a spread-out-mush. So it's possible that Ingo's profile did show the
scheduler more, but it was in the form of much more spread out "noise"
rather than the single spike you saw.

Linus