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    SubjectRe: BFS vs. mainline scheduler benchmarks and measurements

    * Felix Fietkau <nbd@openwrt.org> wrote:

    > Ingo Molnar wrote:
    > > * Felix Fietkau <nbd@openwrt.org> wrote:
    > >
    > >> Ingo Molnar wrote:
    > >> > 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?
    > I did some tests with BFS v230 vs CFS on Linux 2.6.30 on a different
    > MIPS device (Atheros AR2317) with 180 MHz and 16 MB RAM. When running
    > iperf tests, I consistently get the following results when running the
    > transfer from the device to my laptop:
    >
    > CFS: [ 5] 0.0-60.0 sec 107 MBytes 15.0 Mbits/sec
    > BFS: [ 5] 0.0-60.0 sec 119 MBytes 16.6 Mbits/sec
    >
    > The transfer speed from my laptop to the device are the same with BFS
    > and CFS. I repeated the tests a few times just to be sure, and I will
    > check vmstat later.

    Which exact mainline kernel have you tried? For anything performance
    related running latest upstream -git (currently at 202c467) would be
    recommended.

    Ingo


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