Re: statistics infrastructure (in -mm tree) review

[Martin Peschke <mp3@de.ibm.com>]

Greg KH wrote:
> On Thu, Jun 15, 2006 at 12:49:54AM +0200, Martin Peschke wrote:
> > Andi Kleen wrote:
> > > Greg KH <greg@kroah.com> writes:
> > > > > + * exploiters don't update several statistics of the same entity in one 
> > > > > go.
> > > > > + */
> > > > > +static inline void statistic_add(struct statistic *stat, int i,
> > > > > +				 s64 value, u64 incr)
> > > > > +{
> > > > > +	unsigned long flags;
> > > > > +	local_irq_save(flags);
> > > > > +	if (stat[i].state == STATISTIC_STATE_ON)
> > > > > +		stat[i].add(&stat[i], smp_processor_id(), value, incr);
> > >
> > > Indirect call in statistics hotpath?  You know how slow this is 
> > > on IA64 and even on other architectures it tends to disrupt 
> > > the pipeline.
> > Okay, let's try to improve it then. The options here are:
> >
> > a) Replace the indirect function call by a switch statement which directly
> >    calls the add function of the data processing mode chosen by user.
> >    (e.g. simple counter, histogram, utilisation indicator etc.).
> >
> >    No loss in functionality, slightly uglier code, acceptable 
> >    performance(?).
> >    This would be my choice.
>
> Probably best.  Just don't make it an inline function :)

Andi, would this be fine with you?

Thanks, Martin

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