Re: [Xenomai-core] arm ixp: more trouble with recent xenomai

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

Richard Cochran wrote:
> On Sun, Apr 24, 2011 at 10:15:00PM +0200, Gilles Chanteperdrix wrote:
>> some temporary results on the benchmark here:
>> http://www.xenomai.org/~gch/latency-at91sam9263.png
>>
>> The worst case latency seems not to vary much over time, it looks like
>> it is decreasing a bit, but the differences may well be in the
>> measurement noise. Unlocked context switch actually improves the latency.
>>
>> I will update the png as I get new results.
> 
> Gilles,
> 
> That is a very interesting graph. It might be nice to have a
> "performance benchmarks" page on the wiki, including that figure, plus
> the description of the test setup. I can contribute IXP and some
> PowerPC results.

Yes, we should set this up. The xeno-test currently in the head branch
is made to help doing this.

> 
> Regarding the measured performance, the graphs are shaped like the
> letter, H (or like a Bactrian camel, with two humps).
> 
> I appears to me that the peaks of the 2.4.10 lines (red, green) are
> standing clearly to the left of the 2.5.6 lines (blue, purple), by
> about 10 microseconds. I would say that 2.4.10 outperforms 2.5.6, on
> average.

I added the average latencies (except for 2.4.10 with the I-pipe 1.14-04
patch). The peak corresponds roughly to the average "lat max" column in
latency results.

Both the I-pipe version and Xenomai version seem to contribute to the
increased average latency.

The unlocked context switch also improves the worst-case at the expense
of the average.

But there is hope, 2.6.33-1.18-03 introduces pic muting and re-enables
irq in the middle of gpio demuxing, which seems to improve the average
latency.

> 
> The absolute worst case appears to be about the same, or perhaps
> slightly improved in 2.5.6.
> 
> So the differences are not huge, but still I think 2.4.10 is looking
> better.

it is true that 2.4.10 had better average latencies, but the worst case
latencies seem to be improving, and I am afraid this is what we are
aiming at...

-- 
                                                                Gilles.