From: Tim Sander
Date: Mon Aug 15 2011 - 10:05:23 EST


I have more than twice as much cpu load when running the
CONFIG_PREEMPT_RT_FULL=y kernel compared to CONFIG_PREEMPT_RTB=y. First i
thought that might be the difference that one config had softirqs enabled and
the other not. Now i realized that softirqs are already enabled with
CONFIG_PREEMPT_RTB so i don't see a good reason why the CONFIG_PREEMPT_RT_FULL
option should have two times more cpu load than CONFIG_PREEMPT_RTB.

The arm1136 cpu (533Mhz pcm043) has 9.6khz interrupt rate so i surely expect
some load. But i wouldn't expect so much difference between
CONFIG_PREEMPT_RT_FULL and CONFIG_PREEMPT_RTB. So does anybody has an idea
what might a reason to so much more cpu load when going to full preemption?

Besides of the cpu load i also found out that with rt11 i can again wake up
usermode from a IRQF_NO_THREAD waiting on a waitqueue. So the steps outlined
in this mail do not
seem to be neccessary anymore? Or does this create an error and than some high

Best regards

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