[LITMUS^RT] Questions about ft_trace

[Hang Su]

Got you. Thanks.

On Tue, Feb 14, 2012 at 12:25 AM, Glenn Elliott <gelliott at cs.unc.edu> wrote:

> CONFIG_NR_CPUS CPUs controls the maximum number of CPUs your compiled
> Linux kernel can support.  There is no harm in setting this value to be
> greater than the number of actual CPUs in your system-- it may just lead to
> minor waste of memory (the Linux kernel statically allocates memory based
> upon NR_CPUS).
>
> -Glenn
>
>
> On Feb 14, 2012, at 12:18 AM, Hang Su wrote:
>
> 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
>> > _______________________________________________
>> > litmus-dev mailing list
>> > litmus-dev at lists.litmus-rt.org
>> > https://lists.litmus-rt.org/listinfo/litmus-dev
>>
>>
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>
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