Re: Is it possible to trace events and its call stack?

[Masami Hiramatsu <mhiramat@kernel.org>]

On Mon, 16 Jan 2017 16:48:57 +0800
Qu Wenruo <quwenruo@cn.fujitsu.com> wrote:

> 
> 
> At 01/16/2017 10:55 AM, Masami Hiramatsu wrote:
> > On Thu, 12 Jan 2017 15:49:08 +0800
> > Qu Wenruo <quwenruo@cn.fujitsu.com> wrote:
> >
> >> Hi,
> >>
> >> Is it possible to use perf/ftrace to trace events and its call stack?
> >>
> >> [Background]
> >> It's one structure in btrfs, btrfs_bio, I'm tracing for.
> >> That structure is allocated and free somewhat frequently, and its size
> >> is not fixed, so no SLAB/SLUB cache is used.
> >>
> >> I added trace events(or trace points, anyway, just in
> >> include/trace/events/btrfs.h) to trace the allocation and freeing.
> >> Which will output the pointer address of that structure, so I can pair
> >> them, alone with other info.
> >>
> >> Things went well until, I found some structures are allocated but not
> >> freed. (no corresponding trace point is triggered for given address).
> >>
> >> It's possible that btrfs just forget to free it, or btrfs is just
> >> holding it for some purpose.
> >> So kernel memleak detector won't catch the later one.
> >>
> >> That's to say along with the tracepoint data, I still need the call
> >> stack of each calling, to determine the code who leak or hold the pointer.
> >>
> >> Is it possible to do it using perf or ftrace?
> >
> > If you are using ftrace, yes, you can enable stacktrace for each
> > events by setting stacktrace event trigger as below;
> >
> > echo stacktrace > events/btrfs/<your event>/trigger
> >
> > Then ftrace will show the stacktrace data.
> > See /sys/kernel/debug/tracing/README for more details. :)
> 
> That's great!
> 
> The most pure ftrace method!
> 
> I also found perf makes life easier compared to pure ftrace one :)

Should be :)

> Although after some search, I didn't find any equivalent of 
> "function_graph" tracer, which is quite handy to handle small amount of 
> calling time data.
> 
> Does it mean perf tool just doesn't support?

Namhyung had made it. I'm not sure why it is not merged.

https://lwn.net/Articles/570503/

Thank you,

> 
> Thanks,
> Qu
> 
> 
> Thanks,
> Qu
> >
> > Thank you,
> >
> >>
> >> Thanks,
> >> Qu
> >>
> >>
> >> --
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> >
> >
> 
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>