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

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Message-ID: <87h9xxqbm3.fsf@sejong.aot.lge.com>
Date:	Tue, 18 Nov 2014 15:14:12 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	kan.liang@...el.com, acme@...nel.org, a.p.zijlstra@...llo.nl,
	eranian@...gle.com, linux-kernel@...r.kernel.org, mingo@...hat.com,
	paulus@...ba.org, ak@...ux.intel.com
Subject: Re: [PATCH V3 3/3] perf tools: Construct LBR call chain

On Mon, 17 Nov 2014 16:55:53 +0100, Jiri Olsa wrote:
> On Fri, Nov 14, 2014 at 08:44:12AM -0500, kan.liang@...el.com wrote:
>
> SNIP
>
>> +	if (lbr) {
>> +		for (i = 0; i < chain_nr; i++) {
>> +			if (chain->ips[i] == PERF_CONTEXT_USER)
>> +				break;
>> +		}
>> +
>> +		/* 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;
>> +			}
>> +
>> +			for (j = 0; j < mix_chain_nr; j++) {
>> +				if (callchain_param.order == ORDER_CALLEE) {
>> +					if (j < i + 1)
>> +						ip = chain->ips[j];
>> +					else if (j > i + 1)
>> +						ip = lbr_stack->entries[j - i - 2].from;
>> +					else
>> +						ip = lbr_stack->entries[0].to;
>> +				} else {
>> +					if (j < lbr_nr)
>> +						ip = lbr_stack->entries[lbr_nr - j - 1].from;
>> +					else if (j > lbr_nr)
>> +						ip = chain->ips[i + 1 - (j - lbr_nr)];
>> +					else
>> +						ip = lbr_stack->entries[0].to;
>> +				}
>> +
>> +				err = add_callchain_ip(thread, parent, root_al,
>> +						       cpumode, ip);
>> +				if (err)
>> +					goto exit;
>> +			}
>> +			return 0;
>> +		}
>> +	}
>
> also could you please move whole block above into separated function?
> Andi has another change for this function and it's becoming really big.

Agreed.

Thanks,
Namhyung
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