linux-kernel - Re: [PATCH] perf tools: fix callstack entries and nr print message

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Date:   Mon, 9 May 2022 15:45:06 +0200
From:   Jiri Olsa <olsajiri@...il.com>
To:     Chengdong Li <brytonlee01@...il.com>
Cc:     alexey.v.bayduraev@...ux.intel.com, peterz@...radead.org,
        mingo@...hat.com, acme@...nel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
        namhyung@...nel.org, rickyman7@...il.com, adrian.hunter@...el.com,
        irogers@...gle.com, german.gomez@....com,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        ak@...ux.intel.com, likexu@...cent.com, chengdongli@...cent.com
Subject: Re: [PATCH] perf tools: fix callstack entries and nr print message

On Mon, May 09, 2022 at 07:47:43PM +0800, Chengdong Li wrote:
> From: Chengdong Li <chengdongli@...cent.com>
> 
> when generating callstack information from branch_stack(Intel LBR),
> the actual number of callstack entry should be bigger than the number
> of branch_stack, for example:
> 
> 	branch_stack records:
> 		B() -> C()
> 		A() -> B()
> 	converted callstack records should be:
> 		C()
> 		B()
> 		A()
> though, the number of callstack equals
> to the number of branch stack plus 1.
> 
> This patch fix above issue in branch_stack__printf(). For example,
> 
> 	# echo 'scale=2000; 4*a(1)' > cmd
> 	# perf record --call-graph lbr bc -l < cmd
> 
> Before applying this patch, `perf script -D` output:
> 
> 	1220022677386876 0x2a40 [0xd8]: PERF_RECORD_SAMPLE(IP, 0x4002): 17990/17990: 0x40a6d6 period: 894172 addr: 0
> 	... LBR call chain: nr:8
> 	.....  0: fffffffffffffe00
> 	.....  1: 000000000040a410
> 	.....  2: 000000000040573c
> 	.....  3: 0000000000408650
> 	.....  4: 00000000004022f2
> 	.....  5: 00000000004015f5
> 	.....  6: 00007f5ed6dcb553
> 	.....  7: 0000000000401698
> 	... FP chain: nr:2
> 	.....  0: fffffffffffffe00
> 	.....  1: 000000000040a6d8
> 	... branch callstack: nr:6    # which is not consistent with LBR records.
> 	.....  0: 000000000040a410
> 	.....  1: 0000000000408650    # ditto
> 	.....  2: 00000000004022f2
> 	.....  3: 00000000004015f5
> 	.....  4: 00007f5ed6dcb553
> 	.....  5: 0000000000401698
> 	 ... thread: bc:17990
> 	 ...... dso: /usr/bin/bc
> 	bc 17990 1220022.677386:     894172 cycles:
> 			  40a410 [unknown] (/usr/bin/bc)
> 			  40573c [unknown] (/usr/bin/bc)
> 			  408650 [unknown] (/usr/bin/bc)
> 			  4022f2 [unknown] (/usr/bin/bc)
> 			  4015f5 [unknown] (/usr/bin/bc)
> 		    7f5ed6dcb553 __libc_start_main+0xf3 (/usr/lib64/libc-2.17.so)
> 			  401698 [unknown] (/usr/bin/bc)
> 
> After applied:
> 
> 	1220022677386876 0x2a40 [0xd8]: PERF_RECORD_SAMPLE(IP, 0x4002): 17990/17990: 0x40a6d6 period: 894172 addr: 0
> 	... LBR call chain: nr:8
> 	.....  0: fffffffffffffe00
> 	.....  1: 000000000040a410
> 	.....  2: 000000000040573c
> 	.....  3: 0000000000408650
> 	.....  4: 00000000004022f2
> 	.....  5: 00000000004015f5
> 	.....  6: 00007f5ed6dcb553
> 	.....  7: 0000000000401698
> 	... FP chain: nr:2
> 	.....  0: fffffffffffffe00
> 	.....  1: 000000000040a6d8
> 	... branch callstack: nr:7
> 	.....  0: 000000000040a410
> 	.....  1: 000000000040573c
> 	.....  2: 0000000000408650
> 	.....  3: 00000000004022f2
> 	.....  4: 00000000004015f5
> 	.....  5: 00007f5ed6dcb553
> 	.....  6: 0000000000401698
> 	 ... thread: bc:17990
> 	 ...... dso: /usr/bin/bc
> 	bc 17990 1220022.677386:     894172 cycles:
> 			  40a410 [unknown] (/usr/bin/bc)
> 			  40573c [unknown] (/usr/bin/bc)
> 			  408650 [unknown] (/usr/bin/bc)
> 			  4022f2 [unknown] (/usr/bin/bc)
> 			  4015f5 [unknown] (/usr/bin/bc)
> 		    7f5ed6dcb553 __libc_start_main+0xf3 (/usr/lib64/libc-2.17.so)
> 			  401698 [unknown] (/usr/bin/bc)
> 
> Signed-off-by: Chengdong Li <chengdongli@...cent.com>
> ---
>  tools/perf/util/session.c | 24 +++++++++++++++++++-----
>  1 file changed, 19 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
> index f9a320694b85..568a1db98686 100644
> --- a/tools/perf/util/session.c
> +++ b/tools/perf/util/session.c
> @@ -1151,9 +1151,19 @@ static void branch_stack__printf(struct perf_sample *sample, bool callstack)
>  	struct branch_entry *entries = perf_sample__branch_entries(sample);
>  	uint64_t i;
>  
> -	printf("%s: nr:%" PRIu64 "\n",
> -		!callstack ? "... branch stack" : "... branch callstack",
> -		sample->branch_stack->nr);
> +	if (!callstack)
> +		printf("%s: nr:%" PRIu64 "\n", "... branch stack", sample->branch_stack->nr);
> +	else
> +		/* the reason of adding 1 to nr is because after expanding
> +		 * branch stack it generates nr + 1 callstack records. e.g.,
> +		 *         B()->C()
> +		 *         A()->B()
> +		 * the final callstack should be:
> +		 *         C()
> +		 *         B()
> +		 *         A()
> +		 */
> +		printf("%s: nr:%" PRIu64 "\n", "... branch callstack", sample->branch_stack->nr+1);

please use { }

>  
>  	for (i = 0; i < sample->branch_stack->nr; i++) {
>  		struct branch_entry *e = &entries[i];
> @@ -1169,8 +1179,12 @@ static void branch_stack__printf(struct perf_sample *sample, bool callstack)
>  				(unsigned)e->flags.reserved,
>  				e->flags.type ? branch_type_name(e->flags.type) : "");
>  		} else {
> -			printf("..... %2"PRIu64": %016" PRIx64 "\n",
> -				i, i > 0 ? e->from : e->to);
> +			if (i == 0)
> +				printf("..... %2"PRIu64": %016" PRIx64 "\n"
> +				       "..... %2"PRIu64": %016" PRIx64 "\n",
> +						i, e->to, i+1, e->from);
> +			else
> +				printf("..... %2"PRIu64": %016" PRIx64 "\n", i+1, e->from);

same here

thanks,
jirka