Re: 2.6.11, USB: High latency?

[Ingo Molnar <mingo@elte.hu>]

* 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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