Messages in this thread Patch in this message | | | From | Jan Glauber <> | Date | Fri, 11 Mar 2016 11:54:24 +0100 | Subject | Re: [RFC PATCH 1/7] arm64/perf: Basic uncore counter support for Cavium ThunderX |
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On Fri, Feb 12, 2016 at 05:36:59PM +0000, Mark Rutland wrote: > On Fri, Feb 12, 2016 at 05:55:06PM +0100, Jan Glauber wrote:
[...]
> > +int thunder_uncore_event_init(struct perf_event *event) > > +{ > > + struct hw_perf_event *hwc = &event->hw; > > + struct thunder_uncore *uncore; > > + > > + if (event->attr.type != event->pmu->type) > > + return -ENOENT; > > + > > + /* we do not support sampling */ > > + if (is_sampling_event(event)) > > + return -EINVAL; > > + > > + /* counters do not have these bits */ > > + if (event->attr.exclude_user || > > + event->attr.exclude_kernel || > > + event->attr.exclude_host || > > + event->attr.exclude_guest || > > + event->attr.exclude_hv || > > + event->attr.exclude_idle) > > + return -EINVAL; > > We should _really_ make these features opt-in at the core level. It's > crazy that each and every PMU drivers has to explicitly test and reject > things it doesn't support. >
Looking at the exclude_* feature handling in pmu->event_init under arch/ shows lots of differences. Just as an example, exclude_idle returns sometimes -EINVAL, sometimes -EPERM while other archs ignore it and one silently deletes the flag.
So it looks hard to me to move the exclude handling into perf core while keeping the per-arch differences. And if we don't and return an error on the perf_event_open syscall in a newer kernel for an exclude bit that was previously ignored it will be a user-space regression, right?
Looking only at the uncore drivers (plus drivers/bus/arm-cc*) it looks like they all don't support any exclude bits but the handling here differs also. The table shows the current behaviour, X means the requested exclude flag is refused.
user kernel host guest hv idle --------------------------------------------------------------------- x86 uncore intel | X X X X x86 uncore intel snb | X X X X X X x86 uncore intel cqm | X X X X X X x86 uncore intel cstate | X X X X X X x86 uncore intel rapl | X X X X X X x86 uncore amd | X X X X x86 uncore amd iommu | X X X X x86 uncore amd ibs | X X X X X X arm bus cci | X X X X X X arm bus ccn | X X X X ----------------------------------------------------------------------
How about simply adding a helper function to include/linux/perf_event.h that checks if _any_ of the exclude bits is set? We could then simplify the check-for-any exclude flag to:
if (any_exclude_set(event)) return -EINVAL;
What's your opinion?
Jan
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diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index f5c5a3f..0eacdba0 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -849,6 +849,18 @@ static inline bool is_sampling_event(struct perf_event *event) return event->attr.sample_period != 0; } +static inline int any_exclude_set(struct perf_event *event) +{ + if (event->attr.exclude_user || + event->attr.exclude_kernel || + event->attr.exclude_host || + event->attr.exclude_guest || + event->attr.exclude_hv || + event->attr.exclude_idle) + return 1; + return 0; +} + /* * Return 1 for a software event, 0 for a hardware event */
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