linux-kernel - Re: RT wakeup woes in Linux 2.6.31.6 on Mac Mini

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Date:	Fri, 13 Nov 2009 17:24:59 -0800
From:	Greg Steuck <greg@...t.cx>
To:	rostedt@...dmis.org
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: RT wakeup woes in Linux 2.6.31.6 on Mac Mini

Hi Steven,

Thanks for your reply. I believe the answer to my outliers question is
- that's normal. I am lucky enough that 1ms delay is acceptable for my
project and so I can stick with vanilla kernel for now.

On Thu, Nov 12, 2009 at 4:14 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> Have you tried the -rt kernel?

I have now.

> I think you want "wakeup_rt", since that ignores SCHED_OTHER tasks.
> SCHED_OTHER may wake up poorly, and hide the results of your RT task.

Yes, done that now.

> Looks like NEED_RESCHED is set, but interrupts are disabled. This is
> typical for vanilla linux. I really suggest trying out the latest -rt
> patch.

With -rt9 I see a different set of interesting behaviors. I should
mention that my task needs to send network packets. So, I end up
trying to juggle priorities of  irq/27-eth0, sirq-net-rx/1 and my
rxtest tasks. If I make my task higher priority than the other two, I
get interrupts delayed (because my task is being a hog sometimes). If
I go the other way and my task gets lower priority, I end up with my
task not getting to run when there is a lot of network activity which
ultimately kills it.

Thanks
Greg
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