Re: [quad core results] BFS vs. mainline scheduler benchmarks andmeasurements

From: Ingo Molnar
Date: Mon Sep 07 2009 - 09:59:47 EST

* Markus T?rnqvist <mjt@xxxxxxxx> wrote:

> Please Cc me as I'm not a subscriber.
> On Mon, Sep 07, 2009 at 02:16:13PM +0200, Ingo Molnar wrote:
> >
> >Con posted single-socket quad comparisons/graphs so to make it 100%
> >apples to apples i re-tested with a single-socket (non-NUMA) quad as
> >well, and have uploaded the new graphs/results to:
> >
> > kernel build performance on quad:
> >
> [...]
> >
> >It shows similar curves and behavior to the 8-core results i posted
> >- BFS is slower than mainline in virtually every measurement. The
> >ratios are different for different parts of the graphs - but the
> >trend is similar.
> Dude, not cool.
> 1. Quad HT is not the same as a 4-core desktop, you're doing it with 8 cores

No, it's 4 cores. HyperThreading adds two 'siblings' per core, which
are not 'cores'.

> 2. You just proved BFS is better on the job_count == core_count case, as BFS
> says it is, if you look at the graph

I pointed that out too. I think the graphs speak for themselves:

> 3. You're comparing an old version of BFS against an unreleased dev kernel

bfs-208 was 1 day old (and it is a 500K+ kernel patch) when i tested
it against the 2 days old sched-devel tree. Btw., i initially
measured 205 as well and spent one more day on acquiring and
analyzing the 208 results.

There's bfs-209 out there today. These tests take 8+ hours to
complete and validate. I'll re-test BFS in the future too, and as i
said it in the first mail i'll test it on a .31 base as well once
BFS has been ported to it:

> > It's on a .31-rc8 base while BFS is on a .30 base - will be able
> > to test BFS on a .31 base as well once you release it. (but it
> > doesnt matter much to the results - there werent any heavy core
> > kernel changes impacting these workloads.)

> Also, you said on
> "I also tried to configure the kernel in a BFS friendly way, i used
> HZ=1000 as recommended, turned off all debug options, etc. The
> kernel config i used can be found here:
> "
> Quickly looking at the conf you have
> CONFIG_HZ_250=y
> # CONFIG_PREEMPT is not set

Indeed. HZ does not seem to matter according to what i see in my
measurements. Can you measure such sensitivity?

> And other DEBUG.

These are the defaults and they dont make a measurable difference to
these results. What other debug options do you mean and do they make
a difference?

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