[ovs-dev] [PATCH V10] Function tracer to trace all function calls

[Ryan Moats]

"dev" <dev-bounces at openvswitch.org> wrote on 06/17/2016 06:10:32 PM:

> From: Nirapada Ghosh/San Jose/IBM at IBMUS
> To: dev at openvswitch.org
> Date: 06/17/2016 06:10 PM
> Subject: [ovs-dev] [PATCH V10] Function tracer to trace all function
calls
> Sent by: "dev" <dev-bounces at openvswitch.org>
>
> From: Nirapada Ghosh <nghosh at us.ibm.com>
>
> In some circumstances, we might need to figure out where in
> code, the CPU time is being spent most, so as to pinpoint
> the bottleneck and thereby resolve it with proper changes.
> Using '-finstrument-functions' flag, that can be achieved, and
> this patch exactly does that.
>
> There is a python file [generate_ft_report.py] with the patch,
> that may be used to convert this trace output to a human readable
> format with symbol names instead of address and their execution
> times. This tool uses addr2line that expects the executable to
> be built with -g flag.
>
> To enable this feature, ovs needs needs to be configured with
> "--enable-ft" command line argument [i.e. configure --enable-ft]
>
> This instrumentation logs the tracing output in separate log files
> namely func_trace_<pid>.log. It does not use VLOG mechanism for
> logging as that will make the patch very complicated to avoid
> recursion in the trace routine.
>
> This feature starts dumping output, only in debug mode, which means
> ovs-appctl -t <module> vlog/set any:any:dbg should be used to enable
> this logging.
>
> Currently, only ovn-northd, ovn-controller, vswitchd are instrumented.
>
> It is intended to be used for debugging purposes.

I wish this had a test case, but I still haven't thought of how to code
it with one.  I've run make check with this enabled and not and it
looks to pass everything so ...

Acked-by: Ryan Moats <rmoats at us.ibm.com>