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? Would it only hold an "overflow_interrupt_available" flag, or are there other generic capabilities it would be handy to know about? > 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. 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? Vince -- 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/
