Re: [PATCH 1/2] tools, perf: Add a precise event qualifier v2

[Ingo Molnar <mingo@kernel.org>]

* Andi Kleen <andi@firstfloor.org> wrote:

> > Your feature to export 'precise' requirements on events looks useful to 
> > me. We could implement it not by special casing it implicitly but by 
> > saying that if ../format/precise contains something like:
> > 
> >    attr:240-241
> > 
> > then that's a natural extension of the config:X-Y format and should be 
> > interpreted to mean mean 2 bits in the perf attr field. I.e. we could go 
> > beyond the config bitfield.
> > 
> > Basically the whole perf_event_attr can be thought of as a 'giant 
> > bitfield', in which we can specify values to export an enumerated list of 
> > events from the kernel to tooling.
> > 
> > (Using attr:X-Y the config and config1 variants can be expressed as well, 
> > as the config fields are inside the attr structure.)
> > 
> > The positions within the perf_attr are an ABI, so this would work pretty 
> > well.
> 
> Wouldn't we need different bits for each architecture then? 32bit/64bit, 
> some archs with weird alignment rules, maybe different for BE/LE too?
> 
> Ok I suppose it could be somehow auto generated in asm-offsets.c, 
> although I'm not sure how to get a bitfield offset there.

That, or we could indeed start adding specific field names as well, which 
would have a natural position and order.

Thanks,

	Ingo