Re: [PATCH] rcu: convert rcupreempt trace to seq file

Paul E. McKenney
2009-01-11T05:16:18Z

On Sun, Jan 11, 2009 at 06:01:31AM +0100, Frederic Weisbecker wrote:
> On Sun, Jan 11, 2009 at 02:39:40AM +0100, Ingo Molnar wrote:
> >
> > * Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:
> >
> > > On Sat, Jan 10, 2009 at 03:48:46PM +0800, Li Zefan wrote:
> > > > Impact: also fix a bug in show_rcustats()
> > > >
> > > > Use seq file for simplification, and the global buffer and mutex can be
> > > > removed.
> > >
> > > Looks very good, and passes my tests.
> > >
> > > > While doing this, I found rcustats will never show 'ggp' and 'rcc' fields
> > > > due to a bug in show_rcustats().
> > >
> > > Good eyes!
> > >
> > > The only change I ask is that you pull the contents of
> > > rcupreempt_debugfs_init() into the now-one-line rcupreempt_trace_init().
> > >
> > > With that change:
> > >
> > > Tested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > > Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > >
> > > > ---
> > > > kernel/rcupreempt_trace.c | 155 ++++++++++++++++++++-------------------------
> >
> > i think the whole kernel/rcupreempt_trace.c file might be a good candidate
> > for the 'statistical tracing' extensions to ftrace that Frederice is
> > working on.
> >
> > That way there would just be a few tracepoints, and the rest would be done
> > in kernel/tracing/trace_rcupreempt.c, or so.
> > Ingo
>
> Indeed!
>
> The debugfs and seqfile handling and handled in the statistical
> tracing engine.
>
> You just have to provide an iterator for your stat entries through two callbacks:
>
> _ stat_start() -> gives the first entry
> _ stat_next() -> iterates over the next entry
>
> And an output callback
>
> _ stat_show() -> print one entry from your stat list
>
> And two optional things:
>
> _ stat_cmp() -> compare two entries, useful if you want your stats to be sorted
> _ stat_headers() -> provide the first line in your stat file, typically to describe your columns
>
> The last thing you need is to give a name to your trace file.
> You will retrieve it into /debugfs/tracing/trace_stat/your_file_name as a current snapshot
> of your stats.
>
> It is currently used by the branch tracer, and by a pending patch for a new workqueue
> tracer which will provide you a simple example.
>
> If you have any question about how to use it, don't hesitate to ask.

Li Zefan, is this something you would be willing to try? Sounds like
it might be a good addition.

Thanx, Paul