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

[Robert Richter <robert.richter@amd.com>]

On 27.09.10 18:26:27, Matt Fleming wrote:
> 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.

Ok, so then let's implement sh_pmu_name() in
arch/sh/oprofile/common.c, we import asm/perf_event.h to get access to
struct sh_pmu. This could be implemented as a static function then and
we also get rid of this interface thing.

-Robert

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Advanced Micro Devices, Inc.
Operating System Research Center