Re: CONFIG_CRITICAL_IRQSOFF_TIMING

[Gerrit Binnenmars <gerritbinnenmars@wanadoo.nl>]

> Datum: 31/10/07 01:17 AM
> Van: "Steven Rostedt" 
> Aan: "Gerrit Binnenmars" 
> CC: linux-rt-users@vger.kernel.org
> Onderwerp : Re: CONFIG_CRITICAL_IRQSOFF_TIMING
> 
> 
> --
> On Tue, 30 Oct 2007, Gerrit Binnenmars wrote:
> 
> > > Datum: 29/10/07 02:09 PM
> > > Van: "Steven Rostedt"
> > > Aan: "Gerrit Binnenmars"
> > > CC: linux-rt-users@vger.kernel.org
> > > Onderwerp : Re: CONFIG_CRITICAL_IRQSOFF_TIMING
> > >
> > >
> > > --
> > > On Sun, 28 Oct 2007, Gerrit Binnenmars wrote:
> > >
> > > > Hello,
> > > >
> > > > Can someone send me a .config file that shows the options needed to get the interrupt off
> > > > timing values in preempt_max_latency, please. I only see a value of 0 in this file
> > > > I am using kernel 2.6.22.1 with the corresponding rt patch.
> > > >
> > > > Thanks in advance,
> > >
> > > Make sure you have event trace and latency tracing as well as
> > > "Interrupts-off critical section latency timing".
> > >
> > > Then you need to echo 0 > /proc/sys/kernel/preempt_max_latency.
> > >
> > Hello Steve,
> >
> > Thanks for your quick response, but the preempt_max_latency remains 0. Also the latency_hist shows no samples taken.
> > Can you or someone else have a look at the corresponding CONFIG options?
> >
> > CONFIG_LTT_PROBE_LOCKING=m
> > # CONFIG_LTT_PROBE_STACK is not set
> >
> > #
> > # Kernel hacking
> > #
> 
> [...]
> 
> > CONFIG_INTERRUPT_OFF_HIST=y
> > CONFIG_CRITICAL_LATENCY_HIST=y
> > CONFIG_LATENCY_HIST=y
> 
> Turn off all histograms. They will kill any measurements you are taking.
> And yes, you will not get the output from latency_trace that you are
> after.

Steven and Daniel, I tried your suggestion with the following resulsts:
CRITICAL_IRQSOFF_TIMING: preempt_max_latency remains 0 even under load, 
                         cyclictest -b is able to store a trace in /proc/latency_trace
CRITICAL_PREEMPT_TIMING: kernel won´t start at all (vmlinuz is read from tftp server but nothing afterwards)
WAKEUP_TIMING:           is working as expected.

So switching off the histograms is an improvement. For the moment, I can live with this situation 
(especially the cyclictest -b option is very useful),
but I wonder if anyone else has the same problems?

Regards, Gerrit

> 
> -- Steve
> 
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