[PATCH v2 2/3] tools/perf: Add arch neutral function to choose event for perf kvm record

[Anju T Sudhakar <anju@linux.vnet.ibm.com>]

'perf kvm record' uses 'cycles'(if the user did not specify any event) as
the default event to profile the guest.
This will not provide any proper samples from the guest incase of
powerpc architecture, since in powerpc the PMUs are controlled by
the guest rather than the host.

Patch adds a function to pick an arch specific event for 'perf kvm record',
instead of selecting 'cycles' as a default event for all architectures.

For powerpc this function checks for any user specified event, and if there
isn't any it returns invalid instead of proceeding with 'cycles' event.

Signed-off-by: Anju T Sudhakar <anju@linux.vnet.ibm.com>
---

Changes from v1->v2
* Cross-build issue for aarch64, reported by Ravi is fixed.
---

 tools/perf/arch/powerpc/util/kvm-stat.c | 37 +++++++++++++++++++++++++
 tools/perf/builtin-kvm.c                | 12 +++++++-
 tools/perf/util/kvm-stat.h              |  1 +
 3 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/tools/perf/arch/powerpc/util/kvm-stat.c b/tools/perf/arch/powerpc/util/kvm-stat.c
index f9db341c47b6..c55e7405940e 100644
--- a/tools/perf/arch/powerpc/util/kvm-stat.c
+++ b/tools/perf/arch/powerpc/util/kvm-stat.c
@@ -8,6 +8,7 @@
 
 #include "book3s_hv_exits.h"
 #include "book3s_hcalls.h"
+#include <subcmd/parse-options.h>
 
 #define NR_TPS 4
 
@@ -172,3 +173,39 @@ int cpu_isa_init(struct perf_kvm_stat *kvm, const char *cpuid __maybe_unused)
 
 	return ret;
 }
+
+/*
+ * Incase of powerpc architecture, pmu registers are programmable
+ * by guest kernel. So monitoring guest via host may not provide
+ * valid samples. It is better to fail the "perf kvm record"
+ * with default "cycles" event to monitor guest in powerpc.
+ *
+ * Function to parse the arguments and return appropriate values.
+ */
+int kvm_add_default_arch_event(int *argc, const char **argv)
+{
+	const char **tmp;
+	bool event = false;
+	int i, j = *argc;
+
+	const struct option event_options[] = {
+		OPT_BOOLEAN('e', "event", &event, NULL),
+		OPT_END()
+	};
+
+	tmp = calloc(j + 1, sizeof(char *));
+	if (!tmp)
+		return -EINVAL;
+
+	for (i = 0; i < j; i++)
+		tmp[i] = argv[i];
+
+	parse_options(j, tmp, event_options, NULL, PARSE_OPT_KEEP_UNKNOWN);
+	if (!event) {
+		free(tmp);
+		return -EINVAL;
+	}
+
+	free(tmp);
+	return 0;
+}
diff --git a/tools/perf/builtin-kvm.c b/tools/perf/builtin-kvm.c
index 5d2b34d290a3..d03750da051b 100644
--- a/tools/perf/builtin-kvm.c
+++ b/tools/perf/builtin-kvm.c
@@ -1510,11 +1510,21 @@ static int kvm_cmd_stat(const char *file_name, int argc, const char **argv)
 }
 #endif /* HAVE_KVM_STAT_SUPPORT */
 
+int __weak kvm_add_default_arch_event(int *argc __maybe_unused,
+					const char **argv __maybe_unused)
+{
+	return 0;
+}
+
 static int __cmd_record(const char *file_name, int argc, const char **argv)
 {
-	int rec_argc, i = 0, j;
+	int rec_argc, i = 0, j, ret;
 	const char **rec_argv;
 
+	ret = kvm_add_default_arch_event(&argc, argv);
+	if (ret)
+		return -EINVAL;
+
 	rec_argc = argc + 2;
 	rec_argv = calloc(rec_argc + 1, sizeof(char *));
 	rec_argv[i++] = strdup("record");
diff --git a/tools/perf/util/kvm-stat.h b/tools/perf/util/kvm-stat.h
index b3b2670e1a2b..81a5bf4fbc71 100644
--- a/tools/perf/util/kvm-stat.h
+++ b/tools/perf/util/kvm-stat.h
@@ -148,4 +148,5 @@ extern const char *kvm_entry_trace;
 extern const char *kvm_exit_trace;
 #endif /* HAVE_KVM_STAT_SUPPORT */
 
+extern int kvm_add_default_arch_event(int *argc, const char **argv);
 #endif /* __PERF_KVM_STAT_H */
-- 
2.20.1