[LITMUS^RT] Questions about ft_trace

[Hang Su]

Hi Glenn:

Thanks for your quick reply.

First I want to confirm the .config you mentioned is supposed to be located
under /litmus-rt, in which arch, litmus and other main linux directory
reside.  Is that right ?  If so, CONFIG_SCHED_OVERHEAD_TRACE is not set in
.config. It means I have to recompile Litmus kernel by marking
CONFIG_SCHED_OVERHEAD_TRACE item after issuing make menuconfig.

The result of cat /proc/cpuinfo under virtual machine shows only one
processor in my computer, which is different from the one under my real
machine. Probably, I do not allow virtual machine to use two cpus.
CONFIG_NR_CPUS is 8 in my .config. It does not make sense. I do not have so
many cpus. What does    it exactly stand for ?

Thanks

On Mon, Feb 13, 2012 at 11:46 PM, Glenn Elliott <gelliott at cs.unc.edu> wrote:

> Hi Hang Su,
>
> WIth regards to ft_trace, please confirm that
> CONFIG_SCHED_OVERHEAD_TRACE=y in your .config.
>
> With respect to the number of CPUs, is your virtual machine configured to
> run with two CPUs?  If so, what CONFIG_NR_CPUS set to in your .config?
>
> Please note that we recommend using Litmus in a virtual machine only for
> development/debug purposes.  We've found that the time accounting
> mechanisms in virtual machines are not accurate enough for real-time
> performance.
>
> Glad that you're trying Litmus out!
>
> -Glenn
>
>
> On Feb 13, 2012, at 11:20 PM, Hang Su wrote:
>
> > Hi all:
> >
> > LITMUS is new to me. After I installed LITMUS under Oracle Virtual Box
> on my Thinkpad x200, it seems that I can not find ft_trace device under
> /dev/litmus/. Only three devices can be seen under /dev/litmus:
> > ctrl log sched_trace0
> > How could I load a module to create ft_trace device ?
> >
> > Another question is about sched_trace buffer. As said in Tracing and
> Logging tutorial, sched_trace is a per-"processor" buffer. The upbound
> number after sched_trace is  given by num_online_cpus(). My CPU is Intel
> P8600 duo core processors. It is supposed to be two sched_trace buffer. But
> why do i have only one sched_trace buffer under /dev/litmus ?  it is
> because i install LITMUS on virtual machine instead of directly on real
> machine?
> >
> > Thanks
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> > litmus-dev at lists.litmus-rt.org
> > https://lists.litmus-rt.org/listinfo/litmus-dev
>
>
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