linux-kernel - [PATCH] perf tool: arch: arm64: change the way for get_cpuid

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Date:   Thu, 18 Jul 2019 06:21:30 +0000
From:   Joakim Zhang <qiangqing.zhang@....com>
To:     "peterz@...radead.org" <peterz@...radead.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "acme@...nel.org" <acme@...nel.org>,
        "jolsa@...hat.com" <jolsa@...hat.com>,
        "namhyung@...nel.org" <namhyung@...nel.org>
CC:     Frank Li <frank.li@....com>, dl-linux-imx <linux-imx@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Joakim Zhang <qiangqing.zhang@....com>
Subject: [PATCH] perf tool: arch: arm64: change the way for get_cpuid_str()
 function

Now the get_cpuid__str function returns the MIDR string of the first
online cpu from the range of cpus asscociated with the PMU CORE device.

It can work when pass a perf_pmu entity to get_cpuid_str. However, it
will pass NULL via perf_pmu__find_map from metricgroup.c if we want to add
metric group for arm64. When pass NULL to get_cpuid_str, it can't return
the MIDR string.

There are three methods from userspace getting MIDR string for arm64:
1. parse sysfs(/sys/devices/system/cpu/cpu?/regs/identification/midr_el1)
2. parse procfs(/proc/cpuinfo)
3. read the hwcaps(MIDR register) with getauxval(AT_HWCAP)

Perfer to select #3 as it is more simple and direct.

Signed-off-by: Joakim Zhang <qiangqing.zhang@....com>
---
 tools/perf/arch/arm64/util/header.c | 68 +++++++++++------------------
 1 file changed, 25 insertions(+), 43 deletions(-)

diff --git a/tools/perf/arch/arm64/util/header.c b/tools/perf/arch/arm64/util/header.c
index 534cd2507d83..f58f08af0be8 100644
--- a/tools/perf/arch/arm64/util/header.c
+++ b/tools/perf/arch/arm64/util/header.c
@@ -2,64 +2,46 @@
 #include <stdlib.h>
 #include <api/fs/fs.h>
 #include "header.h"
+#include <asm/hwcap.h>
+#include <sys/auxv.h>
 
-#define MIDR "/regs/identification/midr_el1"
 #define MIDR_SIZE 19
 #define MIDR_REVISION_MASK      0xf
 #define MIDR_VARIANT_SHIFT      20
 #define MIDR_VARIANT_MASK       (0xf << MIDR_VARIANT_SHIFT)
 
-char *get_cpuid_str(struct perf_pmu *pmu)
+#define get_cpuid(id) ({					\
+		unsigned long __val;				\
+		asm("mrs %0, "#id : "=r" (__val));		\
+		__val;						\
+	})
+
+char *get_cpuid_str(struct perf_pmu *pmu __maybe_unused)
 {
 	char *buf = NULL;
-	char path[PATH_MAX];
-	const char *sysfs = sysfs__mountpoint();
-	int cpu;
-	u64 midr = 0;
-	struct cpu_map *cpus;
-	FILE *file;
+	unsigned long midr = 0;
 
-	if (!sysfs || !pmu || !pmu->cpus)
+	if (!(getauxval(AT_HWCAP) & HWCAP_CPUID)) {
+		fputs("CPUID registers unavailable\n", stderr);
 		return NULL;
+	}
 
-	buf = malloc(MIDR_SIZE);
-	if (!buf)
+	midr = get_cpuid(MIDR_EL1);
+	if (!midr) {
+		fputs("Failed to get cpuid string\n", stderr);
 		return NULL;
+	}
 
-	/* read midr from list of cpus mapped to this pmu */
-	cpus = cpu_map__get(pmu->cpus);
-	for (cpu = 0; cpu < cpus->nr; cpu++) {
-		scnprintf(path, PATH_MAX, "%s/devices/system/cpu/cpu%d"MIDR,
-				sysfs, cpus->map[cpu]);
-
-		file = fopen(path, "r");
-		if (!file) {
-			pr_debug("fopen failed for file %s\n", path);
-			continue;
-		}
-
-		if (!fgets(buf, MIDR_SIZE, file)) {
-			fclose(file);
-			continue;
-		}
-		fclose(file);
+	/* Ignore/clear Variant[23:20] and
+	 * Revision[3:0] of MIDR
+	 */
+	midr &= (~(MIDR_VARIANT_MASK | MIDR_REVISION_MASK));
 
-		/* Ignore/clear Variant[23:20] and
-		 * Revision[3:0] of MIDR
-		 */
-		midr = strtoul(buf, NULL, 16);
-		midr &= (~(MIDR_VARIANT_MASK | MIDR_REVISION_MASK));
-		scnprintf(buf, MIDR_SIZE, "0x%016lx", midr);
-		/* got midr break loop */
-		break;
-	}
+	buf = malloc(MIDR_SIZE);
+	if (!buf)
+		return NULL;
 
-	if (!midr) {
-		pr_err("failed to get cpuid string for PMU %s\n", pmu->name);
-		free(buf);
-		buf = NULL;
-	}
+	scnprintf(buf, MIDR_SIZE, "0x%016lx", midr);
 
-	cpu_map__put(cpus);
 	return buf;
 }
-- 
2.17.1