[PATCH v2 8/9] perf metrics: Add has_optane literal

[Ian Rogers]

Add literal so that if optane memory isn't installed we can record
fewer events.  The file detection mechanism was suggested by Dan
Williams <dan.j.williams@xxxxxxxxx> in:
https://lore.kernel.org/linux-perf-users/641bbe1eced26_1b98bb29440@xxxxxxxxxxxxxxxxxxxxxxxxx.notmuch/

Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/perf/util/expr.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/tools/perf/util/expr.c b/tools/perf/util/expr.c
index d46a1878bc9e..a43cdda0b044 100644
--- a/tools/perf/util/expr.c
+++ b/tools/perf/util/expr.c
@@ -14,6 +14,7 @@
 #include "util/hashmap.h"
 #include "smt.h"
 #include "tsc.h"
+#include <api/fs/fs.h>
 #include <linux/err.h>
 #include <linux/kernel.h>
 #include <linux/zalloc.h>
@@ -400,6 +401,20 @@ double arch_get_tsc_freq(void)
 }
 #endif
 
+static double has_optane(void)
+{
+	static bool has_optane, cached;
+	const char *sysfs = sysfs__mountpoint();
+	char path[PATH_MAX];
+
+	if (!cached) {
+		snprintf(path, sizeof(path), "%s/firmware/acpi/tables/NFIT", sysfs);
+		has_optane = access(path, F_OK) == 0;
+		cached = true;
+	}
+	return has_optane ? 1.0 : 0.0;
+}
+
 double expr__get_literal(const char *literal, const struct expr_scanner_ctx *ctx)
 {
 	const struct cpu_topology *topology;
@@ -449,6 +464,10 @@ double expr__get_literal(const char *literal, const struct expr_scanner_ctx *ctx
 		result = perf_pmu__cpu_slots_per_cycle();
 		goto out;
 	}
+	if (!strcmp("#has_optane", literal)) {
+		result = has_optane();
+		goto out;
+	}
 
 	pr_err("Unrecognized literal '%s'", literal);
 out:
-- 
2.40.0.348.gf938b09366-goog