linux-kernel - Re: [PATCH v2] perf report: fix off-by-one for non-activation frames

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Message-ID: <20170517051221.GD32691@danjae.aot.lge.com>
Date:   Wed, 17 May 2017 14:12:21 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Milian Wolff <milian.wolff@...b.com>
Cc:     Linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        David Ahern <dsahern@...il.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Yao Jin <yao.jin@...ux.intel.com>, kernel-team@....com
Subject: Re: [PATCH v2] perf report: fix off-by-one for non-activation frames

On Tue, May 16, 2017 at 06:26:47PM +0200, Milian Wolff wrote:
> On Dienstag, 16. Mai 2017 18:17:26 CEST Milian Wolff wrote:
> > On Dienstag, 16. Mai 2017 16:38:29 CEST Namhyung Kim wrote:
> > > On Tue, May 16, 2017 at 10:59:51AM +0200, Milian Wolff wrote:
> > > > As the documentation for dwfl_frame_pc says, frames that
> > > > are no activation frames need to have their program counter
> > > > decremented by one to properly find the function of the caller.
> > > > 
> > > > This fixes many cases where perf report currently attributes
> > > > the cost to the next line. I.e. I have code like this:
> > > > 
> > > > ~~~~~~~~~~~~~~~
> > > > 
> > > >   #include <thread>
> > > >   #include <chrono>
> > > >   
> > > >   using namespace std;
> > > >   
> > > >   int main()
> > > >   {
> > > >   
> > > >     this_thread::sleep_for(chrono::milliseconds(1000));
> > > >     this_thread::sleep_for(chrono::milliseconds(100));
> > > >     this_thread::sleep_for(chrono::milliseconds(10));
> > > >     
> > > >     return 0;
> > > >   
> > > >   }
> > > > 
> > > > ~~~~~~~~~~~~~~~
> > > 
> > > It'd be nice if the test program has a signal frame for verification.
> > 
> > I have pretty much zero experience about signals. Would it be enough to add
> > a signal handler for, say, SIGUSR1 to my test application and then trigger
> > a sleep when that signal is delivered? If that should be enough, I'll write
> > and test it out.
> 
> ~~~~~~~~~~~~~~~
> #include <thread>
> #include <chrono>
> #include <signal.h>
> 
> using namespace std;
> 
> volatile bool run_loop = true;
> 
> void my_handler(int signum)
> {
>     this_thread::sleep_for(chrono::milliseconds(1000));
>     this_thread::sleep_for(chrono::milliseconds(100));
>     this_thread::sleep_for(chrono::milliseconds(10));
>     run_loop = false;
> }
> 
> int main()
> {
>     signal(SIGUSR1, my_handler);
> 
>     while (run_loop) {}
> 
>     return 0;
> }
> ~~~~~~~~~~~~~~~
> 
> This does not properly unwind neither before nor after this patch. I only ever 
> get:
> 
>    100.00%  core.c:0
>             |
>             ---__schedule core.c:0
>                schedule
>                do_nanosleep hrtimer.c:0
>                hrtimer_nanosleep
>                sys_nanosleep
>                entry_SYSCALL_64_fastpath .tmp_entry_64.o:0
>                __nanosleep_nocancel .:0
>                std::this_thread::sleep_for<long, std::ratio<1l, 1000l> > 
> thread:323
> 
> So... should this work? Please tell me how to test this properly.

How did you send the SIGUSR1 to the process?

Anyway it does nothing to do with inlining, right?  I just wrote a
test code below to burn a cpu with or without a signal frame.

  $ nl -ba frame-addr.c
     1	#include <stdio.h>
     2	#include <stdlib.h>
     3	#include <signal.h>
     4	
     5	#define __noinline  __attribute__((noinline))
     6	
     7	__noinline void bar(void)
     8	{
     9	  volatile long cnt = 0;
    10	
    11	  for (cnt = 0; cnt < 100000000; cnt++);
    12	}
    13	
    14	__noinline void foo(void)
    15	{
    16	  bar();
    17	}
    18	
    19	void sig_handler(int sig)
    20	{
    21	  foo();
    22	}
    23	
    24	int main(void)
    25	{
    26	  signal(SIGUSR1, sig_handler);
    27	  raise(SIGUSR1);
    28	
    29	  foo();
    30	  return 0;
    31	}

  $ gcc -O2 -g -fno-optimize-sibling-calls -o frame-addr frame-addr.c

  $ perf record --call-graph dwarf ./frame-addr

  $ perf report -q -g srcline | head -15
      99.88%  frame-addr  frame-addr        [.] bar
              |
              ---bar frame-addr.c:11
                 foo frame-addr.c:16
                 |          
                 |--51.12%--main frame-addr.c:29
                 |          __libc_start_main
                 |          _start
                 |          
                  --48.76%--sig_handler frame-addr.c:21
                            0x33a8f
                            raise .:0
                            main frame-addr.c:29       <--- bad
                            __libc_start_main
                            _start

Note that 'raise' was called at line 27.  It seems that simply
checking current frame fixes it.

Thanks,
Namhyung