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Subject[perf] enable raw OFFCORE_EVENTS for non-perf userspace
Hello

I propose we just enable raw OFFCORE_EVENT support and get it over with.

There is a lot of demand for this from PAPI users, and so we encourage
them to apply the below patch. PAPI supports this out of the box.

The current "block" against using this feature *DOES NOT WORK*.
It silently fails if you try to use the config1 field to set it.

Even worse, if some previous user has set the OFFCORE_RSP_0 msr
(say by running "perf stat -e LLC-load-misses") then
the msr *stays set* and if you try to set the config1 field on your own
it looks like it worked, but instead it is using whatever value the
kernel last used.

So there's a lot of userspace confusion about this, and you can't even
reliably tell if the feature is turned off or not because it fails
silently in unpredictable ways.

Thanks

Vince
vweaver1@eecs.utk.edu

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 4ee3abf..28f9ca9 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -604,12 +604,8 @@ static int x86_setup_perfctr(struct perf_event *event)
return -EOPNOTSUPP;
}

- /*
- * Do not allow config1 (extended registers) to propagate,
- * there's no sane user-space generalization yet:
- */
if (attr->type == PERF_TYPE_RAW)
- return 0;
+ return x86_pmu_extra_regs(event->attr.config, event);

if (attr->type == PERF_TYPE_HW_CACHE)
return set_ext_hw_attr(hwc, event);


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