Re: [PATCH 6/6] sh: oprofile: Use perf-events oprofile backend

[Matt Fleming <matt@console-pimps.org>]

On Tue, Sep 28, 2010 at 12:07:03AM +0200, Robert Richter wrote:
> On 27.09.10 16:01:38, Matt Fleming wrote:
> > On Thu, Sep 16, 2010 at 04:32:54PM +0200, Robert Richter wrote:
> > > > diff --git a/arch/sh/kernel/perf_event.c b/arch/sh/kernel/perf_event.c
> > > > index 2cb9ad5..3c3fc9a 100644
> > > > --- a/arch/sh/kernel/perf_event.c
> > > > +++ b/arch/sh/kernel/perf_event.c
> > > > @@ -59,6 +59,14 @@ static inline int sh_pmu_initialized(void)
> > > >  	return !!sh_pmu;
> > > >  }
> > > >  
> > > > +const char *sh_pmu_name(void)
> > > > +{
> > > > +	if (!sh_pmu)
> > > > +		return NULL;
> > > > +
> > > > +	return sh_pmu->name;
> > > > +}
> > > 
> > > Couldn't we make this a generic function like perf_num_counters()?
> > 
> > Well, ARM doesn't have names as strings for its pmus currently. What's
> > more, ARM wouldn't use it; SH would be the only user of this function. I
> > don't think this one makes sense to be a generic function.
> 
> I didn't catch this with my first review, the function will need an
> EXPORT_SYMBOL_GPL() to allow building modules. This will mean an
> interface extension what should be non-arch. So, for architectures we
> need the pmu name like SH we just implement the generic function. For
> ARM we don't need to provide this function.

Yeah my bad, I just hit this EXPORT_SYMBOL_GPL issue when compiling
oprofile as a module.

> Most of the interface is defined in linux/perf_event.h. We shouldn't
> move this to asm/perf_event.h, so this is one more argument for the
> non-arch implementation.

I'm not advocating moving this function to asm/perf_event.h.

> As the implementation of the function would be optional, why should we
> make it architectural?

I don't see why we should pollute the perf namespace with a function
that is only being used inside the SH oprofile code? There would be
exactly one use of this function and I doubt the perf guys will want
this function exposed. In it's current state, it really is no use to any
architecture other than SH.

We can always add a generic perf_pmu_name() function later if needed,
but it's definitely not needed at the moment.