[PATCH] perf/amd/ibs: Don't set exclude_guest by default

[Ravi Bangoria]

Perf tool sets exclude_guest by default while calling perf_event_open().
Because IBS does not have filtering capability, it always gets rejected
by IBS PMU driver and thus perf falls back to non-precise sampling. Fix
it by not setting exclude_guest by default on AMD.

Before:
  $ sudo ./perf record -C 0 -vvv true |& grep precise
    precise_ip                       3
  decreasing precise_ip by one (2)
    precise_ip                       2
  decreasing precise_ip by one (1)
    precise_ip                       1
  decreasing precise_ip by one (0)

After:
  $ sudo ./perf record -C 0 -vvv true |& grep precise
    precise_ip                       3
  decreasing precise_ip by one (2)
    precise_ip                       2

Reported-by: Kim Phillips <kim.phillips@xxxxxxx>
Signed-off-by: Ravi Bangoria <ravi.bangoria@xxxxxxx>
---
 tools/perf/arch/x86/util/evsel.c | 23 +++++++++++++++++++++++
 tools/perf/util/evsel.c          | 12 +++++++-----
 tools/perf/util/evsel.h          |  1 +
 3 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/tools/perf/arch/x86/util/evsel.c b/tools/perf/arch/x86/util/evsel.c
index 2f733cdc8dbb..7841a49ce856 100644
--- a/tools/perf/arch/x86/util/evsel.c
+++ b/tools/perf/arch/x86/util/evsel.c
@@ -1,8 +1,31 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <stdio.h>
+#include <stdlib.h>
 #include "util/evsel.h"
+#include "util/env.h"
+#include "linux/string.h"
 
 void arch_evsel__set_sample_weight(struct evsel *evsel)
 {
 	evsel__set_sample_bit(evsel, WEIGHT_STRUCT);
 }
+
+void arch_evsel__fixup_new_cycles(struct perf_event_attr *attr)
+{
+	struct perf_env env = {0};
+
+	if (!perf_env__cpuid(&env))
+		return;
+
+	/*
+	 * On AMD, precise cycles event sampling internally uses IBS pmu.
+	 * But IBS does not have filtering capabilities and perf by default
+	 * sets exclude_guest = 1. This makes IBS pmu event init fail and
+	 * thus perf ends up doing non-precise sampling. Avoid it by clearing
+	 * exclude_guest.
+	 */
+	if (env.cpuid && strstarts(env.cpuid, "AuthenticAMD"))
+		attr->exclude_guest = 0;
+
+	free(env.cpuid);
+}
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index dbfeceb2546c..0b4267d4bb38 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -294,7 +294,7 @@ static bool perf_event_can_profile_kernel(void)
 	return perf_event_paranoid_check(1);
 }
 
-struct evsel *evsel__new_cycles(bool precise, __u32 type, __u64 config)
+struct evsel *evsel__new_cycles(bool precise __maybe_unused, __u32 type, __u64 config)
 {
 	struct perf_event_attr attr = {
 		.type	= type,
@@ -305,18 +305,16 @@ struct evsel *evsel__new_cycles(bool precise, __u32 type, __u64 config)
 
 	event_attr_init(&attr);
 
-	if (!precise)
-		goto new_event;
-
 	/*
 	 * Now let the usual logic to set up the perf_event_attr defaults
 	 * to kick in when we return and before perf_evsel__open() is called.
 	 */
-new_event:
 	evsel = evsel__new(&attr);
 	if (evsel == NULL)
 		goto out;
 
+	arch_evsel__fixup_new_cycles(&evsel->core.attr);
+
 	evsel->precise_max = true;
 
 	/* use asprintf() because free(evsel) assumes name is allocated */
@@ -1047,6 +1045,10 @@ void __weak arch_evsel__set_sample_weight(struct evsel *evsel)
 	evsel__set_sample_bit(evsel, WEIGHT);
 }
 
+void __weak arch_evsel__fixup_new_cycles(struct perf_event_attr *attr __maybe_unused)
+{
+}
+
 /*
  * The enable_on_exec/disabled value strategy:
  *
diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index 1f7edfa8568a..764e54c6a23d 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -277,6 +277,7 @@ void __evsel__reset_sample_bit(struct evsel *evsel, enum perf_event_sample_forma
 void evsel__set_sample_id(struct evsel *evsel, bool use_sample_identifier);
 
 void arch_evsel__set_sample_weight(struct evsel *evsel);
+void arch_evsel__fixup_new_cycles(struct perf_event_attr *attr);
 
 int evsel__set_filter(struct evsel *evsel, const char *filter);
 int evsel__append_tp_filter(struct evsel *evsel, const char *filter);
-- 
2.27.0