[yocto] Yocto Realtime tests on beaglebone black

[Bruce Ashfield]

On 2015-02-11 7:35 PM, 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.]

Heh. I know the pain, the giant .configs can give it a fit.

>
> ~ 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.

Agreed.

Bruce

>
>
> 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