linux-kernel - Re: [PATCH -tip v4 0/5] perf script: add BTS analysis features

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Date:	Fri, 20 Jan 2012 16:59:12 +0900
From:	Akihiro Nagai <akihiro.nagai.hw@...achi.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	David Ahern <dsahern@...il.com>, linux-kernel@...r.kernel.org,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	yrl.pp-manager.tt@...achi.com
Subject: Re: [PATCH -tip v4 0/5] perf script: add BTS analysis features

(2012/01/18 20:48), Frederic Weisbecker wrote:
> On Mon, Jan 16, 2012 at 02:21:46PM +0900, Akihiro Nagai wrote:
>> Hi Frederic, David,
>>
>> This patch series adds the functions to analyze BTS logs to perf-script and,
>> makes perf-script more informative version 4.
>> The patches add the following functions.
>>   - Unify the expression to "[unknown]"
>>   - Fix BTS record header to resolve DSOs and symbols of user-space
>>   - Resolve DSOs and symbols for BTS's branch_from addresses
>>   - Show the offset of symbols with the 'offs' field specifier.
>>   - Resolve the real path of [kernel.kallsym] using
>>     '--show-kernel-path' option.
>>
>> Usage:
>> First, get the BTS log with the following command.
>> # perf record -e branches:u -c 1 -d<command>
>>
>> Second, analyze that trace data.
>> # perf script -f ip,addr,sym,offs,dso [--show-kernel-path]
>> This command's output format is:
>> <branch_to addr>  <branch_to function+offset>  <branch_to DSO>  <branch_from addr>  <branch_from function+offset>  <branch_from DSO>
>>
>> Output sample:
>> # perf record -e branches:u -c 1 -d ls
>> [snip]
>> # perf script -f ip,addr,sym,dso,offs --show-kernel-path
>> [snip]
>> 402c1c main+0x0             (/root/bin/ls)       3430c21399 __libc_start_main+0xe9 (/lib64/libc-2.14.so)
>
> I was confused first, looking for the reason why we have a so strange branch flow
> until I realized the format is "to from".
>
> Can we have "from to" instead? This will be much more intuitive. "from =>  to" would be even better.
Exactly.
perf records branch_to information in perf_sample->addr, and branch_from in perf_sample->ip.
And, currently I use the generic function: process_event() in builtin-script.c to print
branch information. This function prints perf_sample->addr before it prints perf_sample->ip.

So, I'm going to add the bts specialized codes to process_event().

static void process_event(...)
{
     <snip>
     print_sample_start(sample, thread, attr);

     if (is_bts_event(attr)) {
         print_sample_bts(...);
         return;
     }

     if (PRINT_FIELD(TRACE))
     <snip>
}

Thank you.
>
> Thanks!
>
>> 40b390 set_program_name+0x0 (/root/bin/ls)           402c41 main+0x25              (/root/bin/ls)
>> 40b390 set_program_name+0x0 (/root/bin/ls) ffffffff814ac5ed irq_return+0x0         (/lib/modules/3.2.0+/build/vmlinux)
>> 401e20 strrchr@...+0x0      (/root/bin/ls)           40b39e set_program_name+0xe   (/root/bin/ls)
>> 401e26 strrchr@...+0x6      (/root/bin/ls)           401e20 strrchr@...+0x0        (/root/bin/ls)
>> 401b80 _init+0x18           (/root/bin/ls)           401e2b strrchr@...+0xb        (/root/bin/ls)
>> 3430813850 _dl_runtime_resolve+0x0 (/lib64/ld-2.14.so) 401b86 _init+0x1e           (/root/bin/ls)
>> [snip]
>
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