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SubjectRe: 2.6.11, USB: High latency?

* kus Kusche Klaus <kus@keba.com> wrote:

> 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.

do these occur under PREEMPT_RT? If yes, do you get any useful trace if
you enable all the tracing options but keep wakeup-timing off:

# CONFIG_WAKEUP_TIMING is not set
CONFIG_PREEMPT_TRACE=y
CONFIG_CRITICAL_PREEMPT_TIMING=y
CONFIG_CRITICAL_IRQSOFF_TIMING=y
CONFIG_CRITICAL_TIMING=y
CONFIG_LATENCY_TIMING=y
CONFIG_LATENCY_TRACE=y
CONFIG_MCOUNT=y

this should catch any type of preempt-off section, irqs-off and
preempt_disable() alike. (unless the tracer has a bug.)

(WAKEUP_TIMING is useful and lightweight but if all other tracing
features are enabled it's a bit pointless, and a bit less accurate.)

Ingo
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