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Subject2.6.11, USB: High latency?
I'm performing realtime latency tests (for details about the hardware
and software, see my mail "[BUG] 2.6.11: Random SCSI/USB errors when
reading from USB memory stick" erlier today).

Even when the errors described in my previous mail does not occur,
massive USB stick transfers cause latencies of 1 to 2 milliseconds,
which is way too much for realtime control systems.

I observe these latencies on a vanilla 2.6.11 at any rtprio (even 99),
and on realtime-preempt-2.6.12-rc1-V0.7.41-11 at low rtprio (1). When
running the program on realtime-preempt-2.6.12-rc1-V0.7.41-11 with
rtprio 99, the latencies are gone, but using a rtprio higher than the
interrupt handlers is not realistic.

Is there anything which can be done about it?

Klaus Kusche
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