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

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Date:	Mon, 17 Nov 2014 16:54:25 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	kan.liang@...el.com
Cc:	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 Fri, Nov 14, 2014 at 08:44:12AM -0500, kan.liang@...el.com wrote:

SNIP

> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
> index f4478ce..335c3a9 100644
> --- a/tools/perf/util/session.c
> +++ b/tools/perf/util/session.c
> @@ -557,15 +557,63 @@ int perf_session_queue_event(struct perf_session *s, union perf_event *event,
>  	return 0;
>  }
>  
> -static void callchain__printf(struct perf_sample *sample)
> +static void callchain__printf(struct perf_evsel *evsel,
> +			      struct perf_sample *sample)
>  {
>  	unsigned int i;
> +	struct ip_callchain *callchain = sample->callchain;
> +	bool lbr = has_branch_callstack(evsel);
>  
> -	printf("... chain: nr:%" PRIu64 "\n", sample->callchain->nr);
> +	if (lbr) {
> +		struct branch_stack *lbr_stack = sample->branch_stack;
> +		u64 kernel_callchain_nr = callchain->nr;
>  
> -	for (i = 0; i < sample->callchain->nr; i++)
> +		for (i = 0; i < kernel_callchain_nr; i++) {
> +			if (callchain->ips[i] == PERF_CONTEXT_USER)
> +				break;
> +		}
> +
> +		if ((i != kernel_callchain_nr) && lbr_stack->nr) {
> +			u64 total_nr;
> +			/*
> +			 * LBR callstack can only get user call chain,
> +			 * i is kernel call chain number,
> +			 * 1 is PERF_CONTEXT_USER.
> +			 *
> +			 * The user call chain is stored in LBR registers.
> +			 * LBR are pair registers. The caller is stored
> +			 * in "from" register, while the callee is stored
> +			 * in "to" register.
> +			 * For example, there is a call stack
> +			 * "A"->"B"->"C"->"D".
> +			 * The LBR registers will recorde like
> +			 * "C"->"D", "B"->"C", "A"->"B".
> +			 * So only the first "to" register and all "from"
> +			 * registers are needed to construct the whole stack.
> +			 */

Andi is using some sanity checks:
http://marc.info/?l=linux-kernel&m=141584447819894&w=2
I guess this could be applied in here, once his patch gets in.

jirka
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