So I ran cyclictest with an idle system and loaded with multiple
instances of cat /dev/zero > /dev/null &
#cyclictest -a 0 -p 99 -m -n -l 100000 -q
I ran this command as shown by Toyoka at the 2014 Linuxcon Japan
[http://events.linuxfoundation.org/sites/events/files/slides/toyooka_LCJ2014_v10.pdf]
to compare against his results for the BBB. I also threw in xenomai
with kernel 3.8 for comparison. For the standard kernel HR timers were
disabled.
[idle]
preempt_rt: min 12 avg: 20 max: 59
standard: min: 8005 avg: 309985955 max: 619963985
xenomai: min: 8 avg: 16: max 803
[loaded]
preempt_rt: min 16 avg: 21 max: 47
standard: min: 15059 avg: 67769851 max: 135530885
xenomai: min: 10 avg: 15: max 839
Actually the preempt_rt results tie up pretty well with Toyooka above,
leading me to conclude theres something off in my code that could be
optimised - what do you guys think.
Also, I ran a test with preempt_rt at 100Hz and there was maybe 10%
improvement in latency.
Steve
On 12/02/2015 00:35, William Mills wrote:
+ meta-ti
Please keep meta-ti in the loop.
[Sorry for the shorting. Thunderbird keep locking up when I tried
replay all in plain text to this message.]
~ 15-02-11, Stephen Flowers wrote:
> Thanks for your input. Here are results of 1000 samples over a
> 10 second period:
>
> Interrupt response (microseconds)
> standard: min: 81, max:118, average: 84
> rt: min: 224, max: 289, average: 231
>
>Will share the .config later once I get on that machine.
Steve I agree the numbers look strange.
There may well be something funny for RT going on for BBB.
TI is just starting to look into RT for BBB.
I would like to see the cyclictest results under heavy system load for
standard and RT kernels. The whole point of RT is to limit the max
latency when the system is doing *anything*.
I am not surprised that the standard kernel has good latency when idle.
As you add load (filessystem is usually a good load) you should see
that max goes up a lot.
Also, as Bruce says, some degradation of min and average and also
general system throughput is expected for RT. That is the trade-off.
I still think the number you are getting for RT seem high but I don't
know what your test is doing in detail. (I did read your explanation.)
cyclictest should give us a standard baseline.
On 02/11/2015 10:25 AM, Bruce Ashfield wrote:
On 15-02-11 03:50 AM, Stephen Flowers wrote:
my bad, here is the patch set.
As for load, only system idle load for the results I posted previously.
Will run some cyclic test next.
One thing that did jump out was the difference in config_hz, you
are taking a lot more ticks in the preempt-rt configuration. If
you run both at the same hz, or with no_hz enabled, it would be
interesting to see if there's a difference.
Bruce
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