linux-kernel - Re: [PATCH 1/3] perf top: Fix freeze on --call-graph flat/folded

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Date:	Fri, 27 Nov 2015 00:10:31 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Kan Liang <kan.liang@...el.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	Wang Nan <wangnan0@...wei.com>
Subject: Re: [PATCH 1/3] perf top: Fix freeze on --call-graph flat/folded

On Thu, Nov 26, 2015 at 03:00:34PM +0100, Jiri Olsa wrote:
> On Thu, Nov 26, 2015 at 10:52:56PM +0900, Namhyung Kim wrote:
> > Hi Jiri,
> > 
> > On Thu, Nov 26, 2015 at 09:38:53AM +0100, Jiri Olsa wrote:
> > > On Thu, Nov 26, 2015 at 04:08:18PM +0900, Namhyung Kim wrote:
> > > > The callchain rbtree is rebuilt periodically, so it needs to
> > > > reinitialize the root everytime.  Otherwise it can be stuck in the
> > > > rbtree insertion with stale pointers.
> > > > 
> > > > Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> > > > ---
> > > >  tools/perf/util/callchain.c | 1 +
> > > >  1 file changed, 1 insertion(+)
> > > > 
> > > > diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
> > > > index fc3b1e0d09ee..564377d2bebf 100644
> > > > --- a/tools/perf/util/callchain.c
> > > > +++ b/tools/perf/util/callchain.c
> > > > @@ -290,6 +290,7 @@ static void
> > > >  sort_chain_flat(struct rb_root *rb_root, struct callchain_root *root,
> > > >  		u64 min_hit, struct callchain_param *param __maybe_unused)
> > > >  {
> > > > +	*rb_root = RB_ROOT;
> > > 
> > > it seems ok, but I did not find how this could be called twice?
> > > 
> > > the only sort I can see is done within:
> > >   __hists__insert_output_entry
> > > 
> > > do we allow resorting of the callchains?
> > 
> > No, but I think it's possible though.
> > 
> > It's called from perf top's display thread.
> 
> ah right.. top ;-) ok
> 
> isn't there analogical issue with the other sorts?
> graph_abs, graph_rel... I dont see that code doing this

The sort_chain_graph_abs/rel() already do this.  Unlike flat/folded
callchains, they put child into each callchain_node's rbtree.  So they
reinitialize node->rb_root in __sort_chain_graph_abs/rel() and reset
rb_root after finishing sort.

Thanks,
Namhyung
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