Re: [Xenomai-help] Xenomai on i7-870

[Philippe Gerum <rpm@xenomai.org>]

On Mon, 2011-06-20 at 16:25 +0100, Jakub Nowacki wrote:
> On 06/20/2011 04:02 PM, Gilles Chanteperdrix wrote:
> > To make proper benchmarks, you should:
> > - let the latency run long
> > - provide some load, you can use the dohell script in xenomai-head to
> > generate the load.
> >
> I've generated a load using 'dd if=/dev/zero of=/dev/null' one for each 
> core (8 in total), which is roughly the way how xeno-test does it. The 
> test was running for 30 min, which is not very long but I should see the 
> long latencies by that time, I think at least.
> 
> > That said, having some spikes is not abnormal. The real question is to
> > know whether the latencies your get are sufficient for your application.
> >
> Well, I think it should be OK for peak latencies < 20 us, that is what 
> I'm getting now.
> 
> >> ioctl(RTTST_RTIOC_SWTEST_CREATE_KTASK): Cannot allocate memory
> >
> > You have to increase CONFIG_XENO_OPT_SYS_STACKPOOLSZ.
> >
> It is 128 Kb now. Should it be more? Is there any (thumb) rule for this 
> value?

Max # of concurrent kernel-based Xenomai threads x stack_size. 8k stack
minimum is a safe bet for x86_64.

Typically, RTDM (driver) tasks in kernel space are Xenomai ones, so you
would need to reserve stack space for each of them in this amount.

The switchtest driver is RTDM-based, and may run a number of RTDM tasks,
depending on the test scenario.

> 
> Best wishes,
> 
> Jakub
> 
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-- 
Philippe.