On Tue, Aug 26, 2025 at 03:08:06PM +0200, Peter Zijlstra wrote:

On Wed, Aug 13, 2025 at 06:01:08PM +0100, Robin Murphy wrote:

quoted

Sampling is inherently a feature for CPU PMUs, given that the thing
to be sampled is a CPU context. These days, we have many more
uncore/system PMUs than CPU PMUs, so it no longer makes much sense to
assume sampling support by default and force the ever-growing majority
of drivers to opt out of it (or erroneously fail to). Instead, let's
introduce a positive opt-in capability that's more obvious and easier to
maintain.

quoted

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 4d439c24c901..bf2cfbeabba2 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h

@@ -294,7 +294,7 @@ struct perf_event_pmu_context;
 /**
  * pmu::capabilities flags
  */
-#define PERF_PMU_CAP_NO_INTERRUPT	0x0001
+#define PERF_PMU_CAP_SAMPLING		0x0001
 #define PERF_PMU_CAP_NO_NMI		0x0002
 #define PERF_PMU_CAP_AUX_NO_SG		0x0004
 #define PERF_PMU_CAP_EXTENDED_REGS	0x0008

@@ -305,6 +305,7 @@ struct perf_event_pmu_context;
 #define PERF_PMU_CAP_EXTENDED_HW_TYPE	0x0100
 #define PERF_PMU_CAP_AUX_PAUSE		0x0200
 #define PERF_PMU_CAP_AUX_PREFER_LARGE	0x0400
+#define PERF_PMU_CAP_NO_INTERRUPT	0x0800

So NO_INTERRUPT was supposed to be the negative of your new SAMPLING
(and I agree with your reasoning).

What I'm confused/curious about is why we retain NO_INTERRUPT?

I see from your other reply that you spotted the next patch does that.

For the sake of other reviewers or anyone digging through the git
history it's probably worth adding a line to this commit message to say:

| A subsequent patch will remove PERF_PMU_CAP_NO_INTERRUPT as this
| requires some additional cleanup.

Mark.