Messages in this thread | | | Date | Sat, 19 Sep 2009 20:01:24 +0200 | From | Ingo Molnar <> | Subject | Re: BFS vs. mainline scheduler benchmarks and measurements |
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* Felix Fietkau <nbd@openwrt.org> wrote:
> Ingo Molnar wrote: > > * Michael Buesch <mb@bu3sch.de> wrote: > > > >> On Tuesday 08 September 2009 09:48:25 Ingo Molnar wrote: > >> > Mind poking on this one to figure out whether it's all repeatable > >> > and why that slowdown happens? > >> > >> I repeated the test several times, because I couldn't really believe > >> that there's such a big difference for me, but the results were the > >> same. I don't really know what's going on nor how to find out what's > >> going on. > > > > Well that's a really memory constrained MIPS device with like 16 MB of > > RAM or so? So having effects from small things like changing details in > > a kernel image is entirely plausible. > > Normally changing small details doesn't have much of an effect. While > 16 MB is indeed not that much, we do usually have around 8 MB free > with a full user space running. Changes to other subsystems normally > produce consistent and repeatable differences that seem entirely > unrelated to memory use, so any measurable difference related to > scheduler changes is unlikely to be related to the low amount of RAM. > By the way, we do frequently also test the same software with devices > that have more RAM, e.g. 32 or 64 MB and it usually behaves in a very > similar way.
Well, Michael Buesch posted vmstat results, and they show what i have found with my x86 simulated reproducer as well (these are Michael's numbers):
procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu---- r b swpd free buff cache si so bi bo in cs us sy id wa 1 0 0 15892 1684 5868 0 0 0 0 268 6 31 69 0 0 1 0 0 15892 1684 5868 0 0 0 0 266 2 34 66 0 0 1 0 0 15892 1684 5868 0 0 0 0 266 6 33 67 0 0 1 0 0 15892 1684 5868 0 0 0 0 267 4 37 63 0 0 1 0 0 15892 1684 5868 0 0 0 0 267 6 34 66 0 0
on average 4 context switches _per second_. The scheduler is not a factor on this box.
Furthermore:
| I'm currently unable to test BFS, because the device throws strange | flash errors. Maybe the flash is broken :(
So maybe those flash errors somehow impacted the measurements as well?
Ingo
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