comments on late joyrides re: rt performance

[victor]

I have been using, for the last weeks joyride-2232 and now I have
joyride-2263. On the other XO, I have a much earlier joyride (1***).
Comparing the RT audio performance of the two, I must say
I am disappointed with how worse it has got.

One of the things I have been playing with is a little MIDI file player
(one of the test/example activities in devel.laptop.org/activities/csndsugui),
which uses a soundfont synthesis engine. On the older system, I
can play most files with only the occasional dropout, generally
quite solidly. But on the later (2232 and 2263), I get many more
dropouts. Every now and then the OS seems to get a break and
go out for coffee or something and the playback gets interrupted for
a few ms. I wondered about a change in
preemption settings in the kernel that comes with the new OS.
For some reason, 2263 seems slightly better than 2232, but I have
to test more (I only updated it this evening)

I will keep testing, but I expect that this will also have an impact
on TamTam. I wonder if more 'aggressive' RT preemption patches
(Ingo Molnar's ones come to mind) would be something worth
considering. I am not sure whether OLPC would entertain the idea,
but I would very much like to see the RT performance improved
one way or another.

Regards

Victor
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