Re: -mm seems significanty slower than mainline on kernbench

["Martin J. Bligh" <mbligh@google.com>]

> > Thanks, but I have that. What do you think those vertical bars on the 
> > graph are for? ;-) They're deviation of 5 runs. I throw away the best 
> > and worst first.
>
>
> Not very good scientific practice :-)


Bollocks to scientific practice ;-) It works, it produces very stable 
results, has done for a few years now. Things like cron or sunspots can 
kick in. Yes, yes, I did stats at University ... but the real world 
doesn't work like that. The visuals in the graph speak for it.

> Looking at the other 6 kernbench graphs, I see that it also occurs for 
> elm3b70 but no others (including elm3b6 and elm3b67).  Are there any 
> differences between the various elm3b systems that could explain this?
Yes. They're all completely different architectures - there's a brief 
description at the top of the main page. elm3b67 should be ignored, nay 
thrown out of the window. It's an unstable POS that randomly loses 
processors. I've removed it from the pages.

elm3b70 is PPC64 (8 cpu)
elm3b6 is x86_64.
elm3b132 is a 4x SMP ia32 Pentium 3.
moe is 16x NUMA-Q (ia32).
gekko-lp1 is a 2x PPC blade.

> > Use the visuals in the graph .. it's very telling. -mm is *broken*.
> > It may well not be the same issue as last time though, I shouldn't
> > have jumped to that conclusion.
>
>
> It's very hard to understand how it could be an issue on a system that 
> doesn't have a lot of abnormally niced (i.e. non zero) tasks that are 
> fairly active as it's now mathematically equivalent to the original in 
> the absence of such tasks.  Do these two systems have many such tasks 
> running?
>
> Would it be possible to get a run with the following patches backed out:
>
> +sched-modified-nice-support-for-smp-load-balancing-fix.patch
> +sched-modified-nice-support-for-smp-load-balancing-fix-fix.patch


Yup, that should prove or disprove it. It's probably something 
completely un-scheduler-related ;-)

M.
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