Re: [PATCH 2/2] sched: make sched_param arugment static variables in some sched_setscheduler() caller

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 06 Jul 2010 19:49:47 -0400 Steven Rostedt <rostedt@goodmis.org> wrote:

> On Tue, 2010-07-06 at 16:12 -0700, Andrew Morton wrote:
> 
> > Well if we're so worried about resource wastage then how about making
> > all boot-time-only text and data reside in __init and __initdata
> > sections rather than hanging around uselessly in memory for ever?
> 
> That would be a patch I would like :-)
> 
> I could probably do that when I get some time.
> 
> > 
> > Only that's going to be hard because we went and added pointers into
> > .init.text from .data due to `struct tracer.selftest', which will cause
> > a storm of section mismatch warnings.  Doh, should have invoked the
> > selftests from initcalls.  That might open the opportunity of running
> > the selftests by modprobing the selftest module, too.
> 
> They are called by initcalls. The initcalls register the tracers and
> that is the time we call the selftest. No other time.

It should all be __init!

> Is there a way that we set up a function pointer to let the section
> checks know that it is only called at bootup?

<sticks his nose in modpost.c for the first time>

There are various whitelisting hacks in there based on the name of the
offending symbol.  Search term: DEFAULT_SYMBOL_WHITE_LIST.

It'd be cleaner to just zap the tracer.selftest field altogether and
run the tests from initcalls if possible?

> > 
> > And I _do_ wish the selftest module was modprobeable, rather than this
> > monstrosity:
> 
> The selftests are done by individual tracers at boot up. It would be
> hard to modprobe them at that time.

No, if tracer_selftest.o was linked into vmlinux then the tests get run
within do_initcalls().  If tracer_selftest.o is a module, then the tests
get run at modprobe-time.  The latter option may not be terribly useful
but it comes basically for free as a reward for doing stuff correctly.

> 
> > #ifdef CONFIG_FTRACE_SELFTEST
> > /* Let selftest have access to static functions in this file */
> > #include "trace_selftest.c"
> > #endif
> > 
> > Really?  Who had a tastebudectomy over there?  At least call it
> > trace_selftest.inc or something, so poor schmucks don't go scrabbling
> > around wondering "how the hell does this thing get built oh no they
> > didn't really go and #include it did they?"
> 
> 
> Well this is also the way sched.c adds all its extra code.

The sched.c hack sucks too.

> Making it
> trace_selftest.inc would make it hard to know what the hell it was.

trace_selftest.i_really_suck?

> And
> also hard for editors to know what type of file it is, or things can be
> missed with a 'find . -name "*.[ch]" | xargs grep blahblah'

Well bad luck.  Of _course_ it makes a mess.  It's already a mess.

How's about just removing the `static' from whichever symbols
tracer_selftest needs?  That'd surely be better than #including a .c
file.

> Yes, the self tests are ugly and can probably go with an overhaul. Since
> we are trying to get away from the tracer plugins anyway, they will
> start disappearing when the plugins do.
> 
> We should have some main selftests anyway. Those are for the TRACE_EVENT
> tests (which are not even in the trace_selftest.c file, and the function
> testing which currently are, as well as the latency testers.
> 
> The trace_selftest.c should eventually be replaced with more compact
> tests for the specific types of tracing.