On Thu, Jul 18, 2019 at 06:21:30AM +0000, Joakim Zhang wrote:
> 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.
Why is this code passing a NULL PMU? What information does it actually
need? Other functions, such as print_pmu_events(), iterate over all PMUs.
> 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.
That's probably terminally broken for heterogeneous systems, so I'm not
at all happy with this patch.
Will
> 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
>
