On Wed, Aug 23, 2017 at 3:47 PM, Will Deacon [off-list ref] wrote:

On Wed, Aug 16, 2017 at 12:40:46PM +0530, Ganapatrao Kulkarni wrote:

quoted

function get_cpuid_str returns MIDR string of the first online
cpu from the range of cpus associated with the pmu core device.

Signed-off-by: Ganapatrao Kulkarni <redacted>
---
 tools/perf/arch/arm64/util/Build    |  1 +
 tools/perf/arch/arm64/util/header.c | 61 +++++++++++++++++++++++++++++++++++++
 2 files changed, 62 insertions(+)
 create mode 100644 tools/perf/arch/arm64/util/header.c

diff --git a/tools/perf/arch/arm64/util/Build b/tools/perf/arch/arm64/util/Build
index cef6fb3..b1ab72d 100644
--- a/tools/perf/arch/arm64/util/Build
+++ b/tools/perf/arch/arm64/util/Build

@@ -1,3 +1,4 @@
+libperf-y += header.o
 libperf-$(CONFIG_DWARF)     += dwarf-regs.o
 libperf-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind.o

diff --git a/tools/perf/arch/arm64/util/header.c b/tools/perf/arch/arm64/util/header.c
new file mode 100644
index 0000000..713ef17
--- /dev/null
+++ b/tools/perf/arch/arm64/util/header.c

@@ -0,0 +1,61 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <api/fs/fs.h>
+#include "header.h"
+
+#define MIDR "/regs/identification/midr_el1"
+#define MIDR_SIZE 128

Why is this so big?

ok, i will reduce it to exact size(19)

quoted

+char *get_cpuid_str(struct perf_pmu *pmu)
+{
+     char *buf = NULL;
+     char *temp = NULL;
+     char path[PATH_MAX];
+     const char *sysfs = sysfs__mountpoint();
+     int cpu;
+     unsigned long long midr = 0;
+     struct cpu_map *cpus;
+     FILE *file;
+
+     if (!sysfs || !pmu->cpus)
+             return NULL;
+
+     buf = malloc(MIDR_SIZE);
+     if (!buf)
+             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_err("fopen failed for file %s\n", path);

pr_debug instead? It's not fatal if a CPU is hotplugged off and you can't
read its midr.

ok

quoted

+                     continue;
+             }
+
+             temp = fgets(buf, MIDR_SIZE, file);
+             if (!temp)
+                     continue;

Do you actually need a temporary variable for this?

ok

quoted

+             fclose(file);
+
+             /* Ignore/clear Variant[23:20] and
+              * Revision[3:0] of MIDR
+              */
+             midr = strtoll(buf, NULL, 16);
+             midr &= (~(0xf << 20 | 0xf));

If midr really needs to be unsigned long long (u64 might be better), then
you need to fix these immediates to have a ULL suffix.

yes, will use u64

Can you use the GENMASK_ULL macro to generate the MIDR mask, or is that
not available here?

it is not defined in tools/include/linux/bitops.h

quoted

+             scnprintf(buf, MIDR_SIZE, "0x%016llx", midr);
+             /* got midr break loop */
+             break;
+     }
+
+     if (!midr) {
+             free(buf);
+             buf = NULL;

If you want the pr_err, here would seem more appropriate because at this
point we've actually failed.

thanks, makes sense.

Will

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thanks
Ganapat