[RFC PATCH 1/7] arm64/perf: Basic uncore counter support for Cavium ThunderX

Jan Glauber
2016-03-11T10:54:24Z

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

---

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
*/