Re: [PATCH V3 3/3] perf tools: Construct LBR call chain

[Namhyung Kim <namhyung@kernel.org>]

On Tue, 18 Nov 2014 14:01:06 +0000, Kan Liang wrote:
>> 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.

Shouldn't it be 18 (16 + 1 + 1) at least?

Thanks,
Namhyung