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From: Jean-Michel Hautbois <jhautbois@gmail.com>
To: linux-rt-users@vger.kernel.org
Subject: Fwd: Question about PREEMPT_RT and wakeup_rt latency
Date: Tue, 25 Jun 2019 15:40:56 +0200	[thread overview]
Message-ID: <CAL8zT=hmt939+2hUN-bine0bk5vq=RMtzdWqsOoog16LRxv2cg@mail.gmail.com> (raw)
In-Reply-To: <CAL8zT=hcP=z_iM+rcUcaTOXLMqVDVn=gbnybp-Q-cmAyKJCzUg@mail.gmail.com>

Hi,

I am currently using for a customer a 5.0.19-rt11 on an i.MX6 and it
works very well ! :)

I have a latency issue, and tried to use wakeup_rt latency to detect
it but I am not sure to really understand the output of ftrace...
From what I understand, the interrupt "irq/28" is having a latency of
~2ms ?? It sound like a very big latency !

And this customer has forced affinity and priorities on its threads,
and I think it could explain such a behaviour ? For instance the task
named "tLaserLo-762" is in fact forced with an affinity of 2 and a
priority of SCHED_FIFO 30.

https://framabin.org/p/?e63c638b5cf2e4ec#GS6ahFDEI/m6vyY2lwafB96vbgA4Skft1d+Dvtry2QI=

I think it gives a very nice example of what preemption really is, but
it can be confusing.
Can it be traced with kernelshark or something else ?

Thanks,
JM

       reply	other threads:[~2019-06-25 13:41 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CAL8zT=hcP=z_iM+rcUcaTOXLMqVDVn=gbnybp-Q-cmAyKJCzUg@mail.gmail.com>
2019-06-25 13:40 ` Jean-Michel Hautbois [this message]
2019-07-03 13:13   ` Fwd: Question about PREEMPT_RT and wakeup_rt latency Sebastian Andrzej Siewior

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