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SubjectRe: [PATCH] x86: add the debugfs interface for the sysprof tool

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

> On Sat, Feb 23, 2008 at 10:11 AM, Andrew Morton
> <akpm@linux-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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