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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:
> >> > * Felix Fietkau <nbd@openwrt.org> wrote:
> >> >> 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.
> >>
> >> I used the OpenWrt-patched 2.6.30. Support for the hardware that I
> >> tested with hasn't been merged upstream yet. Do you think that the
> >> scheduler related changes after 2.6.30 are relevant for non-SMP
> >> performance as well? If so, I'll work on a test with latest upstream
> >> -git with the necessary patches when I have time for it.
> >
> > Dont know - it's hard to tell what happens without basic analysis tools.
> > Is there _any_ way to profile what happens on that system? (Do hrtimers
> > work on it that could be used to profile it?)
>
> oprofile doesn't have any support for it (mips r4k, no generic
> perfcounters), the only usable clock source is a simple cpu cycle
> counter (which is also used for the timer interrupt).

A simple cpu cycle counter ought to be enough to get pretty good
perfcounters support going on that box.

It takes a surprisingly small amount of code to do that, and a large
portion of the perf tooling should then work out of box. Here's a few
example commits of minimal perfcounters support, on other architectures:

310d6b6: [S390] wire up sys_perf_counter_open
2d4618d: parisc: perf: wire up sys_perf_counter_open
19470e1: sh: Wire up sys_perf_counter_open.

Takes about 15 well placed lines of code, if there are no other
complications on MIPS ;-)

Ingo


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