On Thu, Sep 12, 2013 at 07:36:17PM +0200, Andi Kleen 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 Since we currently have the pattern $name:bits to mean perf_event_attr::$name the above would imply and create a possible collision with perf_event_attr::attr. If we're going to do this I'd propose using something like _:240-241, for while '_' is a valid name in C its not something we're ever going to allow in perf_event_attr. > > 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? Typically PMU drivers are per arch and all the format stuff is per pmu driver so I'd not worry about that just yet. But yes, while the perf_event_attr thing is ABI its not identical across archs. > 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. Yes, that is an unfortunate situation. I (and either Acme or Jolsa) tried wrapping the bitfield in an anonymous union to create a named variable for the entire u64 but older GCC completely fails with that. -- To unsubscribe from this list: send the line "unsubscribe trinity" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
