linux-kernel - Re: [PATCH] x86: add the debugfs interface for the sysprof tool

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Date:	Sat, 23 Feb 2008 13:22:22 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org, sandmann@...hat.com, tglx@...x.de,
	hpa@...or.com
Subject: Re: [PATCH] x86: add the debugfs interface for the sysprof tool


* Pekka Enberg <penberg@...helsinki.fi> wrote:

> On Sat, Feb 23, 2008 at 10:11 AM, Andrew Morton
> <akpm@...ux-foundation.org> wrote:
> >  Seems a poor idea to me.  Sure, oprofile is "hard to set up", but not if
> >  your distributor already did it for you.
> 
> Have you tried sysprof? It's really nice to setup and use compared to 
> oprofile when profiling user-space.

yes, it's very nice and very usable - and that's all that matters 
really. It's almost a _duty_ of the mainstream kernel to include that 
trivial 200 lines of sysprof code, given how poor instrumentation 
support is on Linux.

As a comparison, here's a session of a newbie developer, meeting 
oprofile for the first time in his life (using a fresh package, 
oprofile-0.9.3-6.fc8):

  ---------------------->
  [ Newbie: WTF, no GUI tool? ]
  [ Narrator: we lose 90% of the developers at this point. ]
  [ Newbie is adventurous and has heard about opcontrol and tries it. ]
 
  # opcontrol

  [ Newbie sees tons of output. User scratches head. After looking 
    around, finds the following option listed:
    "-s/--start       start data collection". That must be it! ]

  # opcontrol -s
  No vmlinux file specified. You must specify the correct vmlinux file, e.g.
  opcontrol --vmlinux=/path/to/vmlinux
  If you do not have a vmlinux file, use
  opcontrol --no-vmlinux
  Enter opcontrol --help for full options

  [ Newbie: WTF? Doesnt oprofile think that what I want to do is to 
    profile ... the currently running kernel, wherever a kernel is 
    and whatever a vmlinux might be?? ]

  [ Narrator: At this point oprofile has confused about 99% of all 
    user-space developers who have no freaking idea about what a vmlinux 
    is. ]

  [ Newbie user figures that --no-vmlinux might be the right option: ]

  # opcontrol -s --no-vmlinux
  Option "--setup" not valid with "-s".

  [ Newbie: WTF? what not valid? Why should i care? Damnit, i only want 
    to profile stuff!!! ]

  [ The newbie user eventually finds out that opcontrol help text is 
    buggy and that -s does not mean --start, but --setup. ]

  [ Narrator: we now have lost 99.99% of the first-time users. ]

  [ Newbie, armed with this nontrivial piece of information: ]

  # opcontrol --start --no-vmlinux
 
  Using default event: CPU_CLK_UNHALTED:100000:0:1:1
  Using 2.6+ OProfile kernel interface.
  Using log file /var/lib/oprofile/samples/oprofiled.log
  Daemon started.
  Profiler running.

  [ Newbie: wow, it's working! Lets start an infinite loop and lets try 
    this opreport thing: ]

  # opreport

   CPU_CLK_UNHALT...|
     samples|      %|
   ------------------
       160405 82.9309 loop

  [ Newbie: hm, i see where the overhead is - but which function is 
    calling it? ]

  [ Newbie user wants to restart profiling and figures that
    opcontrol --reset will do that: ]

  # opcontrol --reset
  Signalling daemon... done

  [ GREAT! It even said "done". Now lets see our new profile: ]

  # opreport
  opreport error: No sample file found: try running opcontrol --dump
  or specify a session containing sample files

  [ Newbie: WTF???? ]

  [ Narrator: we've now lost 99.99999% of the testers at this point. The 
    reamining 10 kernel developers still using oprofile have written up 
    all the commands to the back of their keyboards, for easy reference. ]
  <----------------------

We should hang our collective heads in shame. Oprofile is an utter joke 
in terms of usability. It had 5-10 years to get its stuff together and 
didnt.

200 lines of totally isolated sysprof code is the least thing we can do 
which we _must do_ to help our users.

	Ingo
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