[LITMUS^RT] Questions about ft_trace

[Glenn Elliott]

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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