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SubjectRe: [PATCH]sched: Isochronous class v2 for unprivileged soft rt scheduling
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Werner Almesberger <wa@almesberger.net> writes:

> [ Cc:s trimmed, added abiss-general ]
>
> Con Kolivas wrote:
>> Possibly reiserfs journal related. That has larger non-preemptible code
>> sections.
>
> If I understand your workload right, it should consist mainly of
> computation, networking (?), and disk reads.

The jack_test3.2 is basically a multiprocess realtime audio test. A
fair amount of computation, signifcant task switch overhead, but
most I/O is to the sound card.

There's some disk activity starting clients and probably some other
system activity in the background.

> I don't know much about ReiserFS, but in some experiments with ext3,
> using ABISS, we found that a reader application competing with best
> effort readers would experience worst-case delays of dozens of
> milliseconds.
>
> They were caused by journaled atime updates. Mounting the file
> system with "noatime" reduced delays to a few hundred microseconds
> (still worst-case).

Interesting. Worth a try to verify. Con was seeing a 6msec delay
every 20 seconds. This was devastating to the test, which tries to
run a full realtime audio cycle every 1.45msec.
--
joq
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