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Subject[PATCH v1 3/5] perf tools arm64: Add support for get_cpuid() function
Date
The get_cpuid() function returns the MIDR string of the first CPU.

Cc: Ganapatrao Kulkarni <ganapatrao.kulkarni@cavium.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>

---
When recording, perf will write host's cpuid (through get_cpuid()) into
perf.data.guest file:

__cmd_record
record__finish_output
perf_session__write_header
perf_header__adds_write
do_write_feat (type == HEADER_CPUID)
write_cpuid

When reporting, perf will read cpuid from perf.data.guest file:

read_events
perf_session__new
perf_session__open
perf_session__read_header
perf_header__process_sections
perf_file_section__process
process_cpuid

I'm not familiar with ARM ID register usage, and how does perf code make
use of get_cpuid() function. If we left get_cpuid() unimplemented on
arm64 (we have a default implementation in tools/perf/util/header.c),
'perf kvm stat report' will failed with following error:
"Failed to look up CPU type"

I will read the code further, and any comments or suggestions from both
sides (arm64 & perf) will be appreciated.

---
tools/perf/arch/arm64/util/header.c | 74 +++++++++++++++++++++++--------------
1 file changed, 47 insertions(+), 27 deletions(-)

diff --git a/tools/perf/arch/arm64/util/header.c b/tools/perf/arch/arm64/util/header.c
index 534cd25..5c17b86 100644
--- a/tools/perf/arch/arm64/util/header.c
+++ b/tools/perf/arch/arm64/util/header.c
@@ -9,17 +9,56 @@
#define MIDR_VARIANT_SHIFT 20
#define MIDR_VARIANT_MASK (0xf << MIDR_VARIANT_SHIFT)

-char *get_cpuid_str(struct perf_pmu *pmu)
+/* Return value of midr_el1 if success, else return 0. */
+static int read_midr_el1(char *buf, int cpu_nr)
{
- char *buf = NULL;
char path[PATH_MAX];
const char *sysfs = sysfs__mountpoint();
+ u64 midr = 0;
+ FILE *file;
+
+ if (!sysfs)
+ return 0;
+
+ scnprintf(path, PATH_MAX, "%s/devices/system/cpu/cpu%d"MIDR,
+ sysfs, cpu_nr);
+
+ file = fopen(path, "r");
+ if (!file) {
+ pr_debug("fopen failed for file %s\n", path);
+ return 0;
+ }
+
+ if (!fgets(buf, MIDR_SIZE, file)) {
+ fclose(file);
+ return 0;
+ }
+ fclose(file);
+
+ /* 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);
+
+ return midr;
+}
+
+int get_cpuid(char *buffer, size_t sz __maybe_unused)
+{
+ if (read_midr_el1(buffer, 0))
+ return 0;
+
+ return -1;
+}
+
+char *get_cpuid_str(struct perf_pmu *pmu)
+{
+ char *buf = NULL;
int cpu;
u64 midr = 0;
struct cpu_map *cpus;
- FILE *file;

- if (!sysfs || !pmu || !pmu->cpus)
+ if (!pmu || !pmu->cpus)
return NULL;

buf = malloc(MIDR_SIZE);
@@ -29,29 +68,10 @@ char *get_cpuid_str(struct perf_pmu *pmu)
/* 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 = strtoul(buf, NULL, 16);
- midr &= (~(MIDR_VARIANT_MASK | MIDR_REVISION_MASK));
- scnprintf(buf, MIDR_SIZE, "0x%016lx", midr);
- /* got midr break loop */
- break;
+ midr = read_midr_el1(buf, cpus->map[cpu]);
+ if (midr)
+ /* got midr break loop */
+ break;
}

if (!midr) {
--
1.8.3.1

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