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

[Li Zefan <lizf@cn.fujitsu.com>]

> 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.
> 

Hi Frederic,

I've converted rcupreempt to use trace points, but I don't see much advantage to use
trace stat instead of using seq_file directly.. And can you add support to allow
me to provide stat_show() only ? I think it's common that the stat file has only
one entry.


Regards
Li Zefan