[PATCH 07/10] perf tools: Separate exclude_hv fallback

[Namhyung Kim]

The exclude_hv was added in the evsel__fallback() in the commit
4ec8d984895fef43a ("perf record: Fix priv level with branch sampling
for paranoid=2") to address branch stack samples on Intel PMUs.
As some other PMUs might not support that, let's separate the bit from
exclude_kernel to make sure it can add the bit only if required.

Technically it should change the modifier string at the end of the
event name.  ":u" is for exclude_kernel + exclude_hv, so it should be
":uh" if it has exclude_kernel only.  That means the default events for
regular users will looks like "cycles:Puh" (for perf record) or
"instructions:uh" (for perf stat).  But I'm not sure if it's worth the
trouble so I didn't touch the name in this patch.

Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
---
 tools/perf/util/evsel.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 1a4f52767942e5ad..c5df45bb74dfc1b5 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -3389,10 +3389,20 @@ bool evsel__fallback(struct evsel *evsel, struct target *target, int err,
 		free(evsel->name);
 		evsel->name = new_name;
 		scnprintf(msg, msgsize, "kernel.perf_event_paranoid=%d, trying "
-			  "to fall back to excluding kernel and hypervisor "
-			  " samples", paranoid);
+			  "to fall back to excluding kernel samples", paranoid);
 		evsel->core.attr.exclude_kernel = 1;
-		evsel->core.attr.exclude_hv     = 1;
+
+		return true;
+	} else if (err == EACCES && !evsel->core.attr.exclude_hv &&
+		   (paranoid = perf_event_paranoid()) > 1) {
+		/* If event has exclude user then don't exclude hv. */
+		if (evsel->core.attr.exclude_user)
+			return false;
+
+		/* Intel branch stack requires exclude_hv */
+		scnprintf(msg, msgsize, "kernel.perf_event_paranoid=%d, trying "
+			  "to fall back to excluding hypervisor samples", paranoid);
+		evsel->core.attr.exclude_hv = 1;
 
 		return true;
 	} else if (err == EOPNOTSUPP && !evsel->core.attr.exclude_guest &&
-- 
2.46.0.469.g59c65b2a67-goog