[LITMUS^RT] Feather-trace tools

[Glenn Elliott]

On Jan 27, 2014, at 6:13 AM, Chandrasekaran Sivakumar <chandru.a6 at gmail.com> wrote:

> Hi,
> I tried using feather trace tools. 
> sudo ./ftcat /dev/litmus/ft_trace0 CXS_START CXS_END SCHED_START SCHED_END SCHED2_START SCHED2_END > my_trac
> I got the error as following:
> Error: could not open feathertrace device (/dev/litmus/ft_trace0): No such file or directory
> 
> What's the issue ?
>  
> Regards,
> chandru

What do you see in /dev/litmus?  Do you see an ft_trace device?  If you don’t, then you Litmus kernel was compiled without ft_trace support.  To enable this, in “make menuconfig” enable the following options:

LITMUS^RT > Tracing > Feather-Trace Infrastructure (CONFIG_FEATHER_TRACE)
LITMUS^RT > Tracing > Record timestamps for overhead measurements (CONFIG_SCHED_OVERHEAD_TRACE)
LITMUS^RT > Tracing > Buffer size for Feather-Trace overhead data (CONFIG_SCHED_OVERHEAD_TRACE_SHIFT)

If any of those options are unavailable, then check litmus/Kconfig and investigate the prerequisite configuration options that must be set to make the ft_trace options available.

For CONFIG_SCHED_OVERHEAD_TRACE_SHIFT, pick a size for the ft_trace ring buffer.  Unless you’re on an embedded system, you should probably pick the largest allowable size.

If you’re using the Litmus-staging branch from github, then ft_trace works a little differently—improvements were make to improve scalability.  More info here: https://lists.litmus-rt.org/pipermail/litmus-dev/2014/000784.html

-Glenn