linux-kernel - Re: [PATCH -tip v3 0/6] perf: Introduce branch sub commands

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Date:	Fri, 1 Apr 2011 16:43:15 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Akihiro Nagai <akihiro.nagai.hw@...achi.com>
Cc:	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	2nddept-manager@....hitachi.co.jp
Subject: Re: [PATCH -tip v3 0/6] perf: Introduce branch sub commands

On Thu, Mar 24, 2011 at 08:31:37PM +0900, Akihiro Nagai wrote:
> Hi,
> 
> This patch series provides the commands 'perf branch record' and 'perf branch trace'
> version 3. These commands record and analyze a BTS (Branch Trace Store) log.
> And, they provide the interface to use BTS log for application developers.
> 
> BTS is a facility of Intel x86 processors, which records the address of
> 'branch to/from' on every branch/jump instruction and interrupt.
> This facility is very useful for developers to test their software,
> for example, coverage test, execution path analysis, dynamic step count ...etc.
> These test tools have a big advantage, which user doesn't have to modify target
> executable binaries, because the BTS is a hardware feauture.
> 
> But, there are few applications using BTS. Reasons I guess are ...
>  - Few people know what BTS is.
>  - Few people know how to use BTS on Linux box.
>  - It's hard to analyze the BTS log because it includes just a series of addresses.
> 
> So, I want to provide a user-friendly interface to BTS for application developers.
> 
> 
>  About new sub commands
> ========================
> 'perf branch record' provides an easy way to record BTS log.
> Usage is 'perf branch record <command>'.  This command is just an alias to
> 'perf record -e branches:u -c 1 <command>'. But, new one is more simple and
> more intuitive.
> 
> 'perf branch trace' can parse and analyze recorded BTS log and print various
> information of execution path. This command can show address, pid, command name,
> function+offset, file path of elf.
> You can choose the printed information with option.
> 
> Example: 'perf branch trace'
> function+offset
> irq_return+0x0  => _start+0x0
> irq_return+0x0  => _start+0x0
> _start+0x3      => _dl_start+0x0
> irq_return+0x0  => _dl_start+0x0
> irq_return+0x0  => _dl_start+0x26
> irq_return+0x0  => _dl_start+0x2d
> _dl_start+0x71  => _dl_start+0x93
> _dl_start+0x97  => _dl_start+0x78
> ...
> 
> This is the default behavior of 'perf branch trace'. It prints function+offset.
> 
> 
> Example2: 'perf branch -cas trace'
> command address            function+offset                  
> ls      0xffffffff8146fe0e irq_return+0x0  => ls   0x0000003806200b20 _start+0x0

You probably want to display the comm (and/or the pid/tid) only once. Those are not
going to change between the source and destination.
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