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Subject: Re: Latency data - 2.6.14-rc3-rt13
From: Daniel Walker <dwalker@mvista.com>
To: Mark Knecht <markknecht@gmail.com>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
       Lee Revell <rlrevell@joe-job.com>
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Date: Mon, 10 Oct 2005 14:44:33 -0700
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On Mon, 2005-10-10 at 14:28 -0700, Mark Knecht wrote:
> On 10/10/05, Mark Knecht <markknecht@gmail.com> wrote:
> <SNIP>
> > > then goto Kernel Hacking and select
> > > "Interrupts-off critical section latency timing"
> > > Then select "Latency tracing"
> 
> Only had to turn on Latency Tracing. The others I had on...
> 
> <SNIP>
> > >
> > > Daniel
> >
> > Will do. Building now. I'll be back later.
> >
> 
> Unfortunately I didn't think I'd be back this fast. I built the new
> kernel and rebooted. The boot starts, gets down to the point where it
> tells me that the preempt debug stuff is on, and then jumps to an
> endlessly repeating error message:
> 
> init[1]: segfault at ffffffff8010fce0 rip ffffffff8010fce0 rsp
> 00007fffffcb09b8 error 15
> 
> This error repeasts endlessly until I reboot.
> 
> Good thing I had another kernel I could boot back into! ;-)
> 
> So, something isn't happy. Is this a -rt thing or a kernel issue?

Hmm, it looks like latency tracing doesn't work on x86_64 .. I guess
you'll have to wait till someone fixes it .

Another option is to turn off "Latency Tracing" then reboot, like it was
before but w/o the histogram. Then run,

"echo 0 > /proc/sys/kernel/preempt_max_latency"

Whenever a new maximum latency is observed it will log it with a stack
trace in the system logs. You can report that back here on LKML . 

You can view the system log with the command "dmesg" , I think .

Daniel

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