linux-kernel - RE: [PATCH V3 3/3] perf tools: Construct LBR call chain

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Date:	Tue, 18 Nov 2014 14:01:06 +0000
From:	"Liang, Kan" <kan.liang@...el.com>
To:	Namhyung Kim <namhyung@...nel.org>
CC:	"acme@...nel.org" <acme@...nel.org>,
	"jolsa@...hat.com" <jolsa@...hat.com>,
	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"eranian@...gle.com" <eranian@...gle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"paulus@...ba.org" <paulus@...ba.org>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>
Subject: RE: [PATCH V3 3/3] perf tools: Construct LBR call chain



> On Fri, 14 Nov 2014 08:44:12 -0500, kan liang wrote:
> > +		/* LBR only affects the user callchain */
> > +		if (i != chain_nr) {
> > +			struct branch_stack *lbr_stack = sample-
> >branch_stack;
> > +			int lbr_nr = lbr_stack->nr;
> > +			/*
> > +			 * LBR callstack can only get user call chain.
> > +			 * The mix_chain_nr is kernel call chain
> > +			 * number plus LBR user call chain number.
> > +			 * i is kernel call chain number,
> > +			 * 1 is PERF_CONTEXT_USER,
> > +			 * lbr_nr + 1 is the user call chain number.
> > +			 * For details, please refer to the comments
> > +			 * in callchain__printf
> > +			 */
> > +			int mix_chain_nr = i + 1 + lbr_nr + 1;
> > +
> > +			if (mix_chain_nr > PERF_MAX_STACK_DEPTH) {
> > +				pr_warning("corrupted callchain.
> skipping...\n");
> > +				return 0;
> > +			}
> 
> I'm not sure whether this is really a corrupted callchain.  If a single chain is
> greater than the max it should be corrupted, but we're now summing up
> with other values..
> 
> What about checking callchain_nr and lbr_nr separately or mix_nr with
> 2*max?

The lbr_nr max is 16. I will change it to max+16.

Thanks,
Kan

> 
> Thanks,
> Namhyung
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