On Mon, Jan 13, 2014 at 11:55:17PM -0500, Vince Weaver wrote: > On Fri, 10 Jan 2014, Peter Zijlstra wrote: > > > On Thu, Jan 09, 2014 at 11:08:47PM -0500, Vince Weaver wrote: > > > On Thu, 9 Jan 2014, Will Deacon wrote: > > > > > > > I'd rather see it in the generic code if at all possible. Maybe we > > > > could add > > > > a flags field to perf_pmu_register? > > > > > > I can look into adding the check in generic code. > > > > Adding something like this to the generic code would mean adding a > > struct pmu capabilities field and visiting all existing PMU > > implementations to properly fill this out. > > I don't see an existing pmu capabilities struct... or do you mean > coming up with one?
Yeah, adding one. > Would it only hold an "overflow_interrupt_available" flag, or are > there other generic capabilities it would be handy to know about? Possible (other) flags could be: PMU_HAS_INT -- would allow sampling events PMU_HAS_PRECISE -- would allow any ::precise value PMU_HAS_FILTER -- would allow all os/user/etc. flags > > There's a number of hardware PMU implementations that do not have an > > interrupt and would need to set this flag. > > Well that can be added gradually, right? Things wouldn't get any worse if > we add a generic check without auditing all code, things will just behave > the same as before for those architectures. Right, doing a sweep once every so often is useful to find more patterns though. > There is some subtlety here though. On ARM (or at least rasp-pi) the > overflow hardware is there, just no interrupt is hooked up. So things > like counter overflow are handled as long as overflows aren't faster than > context switch time. It's just sampled events aren't possible. > > On architectures without overflow support at all (I've had such hardware; > some SPARC machines, the Playstation 3 hypervisor) then counter overflow > isn't possible without a periodic timer (sort of like what is done with > Intel uncore). Is that something that should be in generic code too? Maybe yeah, if there's enough replication of this it certainly makes sense to lift it into generic code. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
