Re: [Jack-Devel] jack dsp load calculation

On 12/23/2015 08:29 PM, Paul Davis wrote:
> On Wed, Dec 23, 2015 at 10:35 AM, Robin Gareus <[hidden]> wrote:
> 
>>
>> Short spikes, which are in most cases the cause for xruns, are simply
>> ignored in the calculation: For them to show up, currently three
>> criteria must be met: The spike must be in the last 32 jack-cycles, be >
>> 95% and the control application must read the value near the end of
>> those 32 cycles (see [1], very high LPF).
>>
> 
> there is a justification for this. your paragraph starts with the claim
> that these short spikes correspond to xruns. there is a counter-claim that
> they represent measurement error.
> 
> i'm in full agreement with your argument *if* it can be shown that the
> spikes are not measurement errors

If jack can't keep track of the time properly we have much more serious
issues.

jackd on POSIX systems is robust. The time is queried in a high priority
thread and jack2 offers `--clocksource` for a user to tweak it if needed.

> (or, alternatively, that measurement
> error is best excluded via a different heuristic).

Yes, outliers - e.g jumps on suspend/resume or leap-seconds
(non-monotonic clock) must be skipped.

In Ardour we ended up ignoring negative deltas and jumps larger than 10
times the cycle-length. (This in particular is relevant for AMD machines
and Windows XP where the clock is per cpu-core.)

Early 4.X had a sigma-cut (based on running variance) but that turned
out too be too statistical for the case of displaying peak-computing power.

so long,
robin

1451130215.18422_0.ltw:2,a <567E7D5E.60404 at gareus dot org>