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Date: Fri, 19 Jul 2019 08:29:12 +0000
From: Joakim Zhang <qiangqing.zhang@....com>
To: Will Deacon <will@...nel.org>
CC: "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>,
Frank Li <frank.li@....com>, dl-linux-imx <linux-imx@....com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"mark.rutland@....com" <mark.rutland@....com>
Subject: RE: [PATCH] perf tool: arch: arm64: change the way for
get_cpuid_str() function
> -----Original Message-----
> From: Will Deacon <will@...nel.org>
> Sent: 2019年7月19日 15:55
> To: Joakim Zhang <qiangqing.zhang@....com>
> Cc: peterz@...radead.org; mingo@...hat.com; acme@...nel.org;
> jolsa@...hat.com; namhyung@...nel.org; Frank Li <frank.li@....com>;
> dl-linux-imx <linux-imx@....com>; linux-kernel@...r.kernel.org;
> mark.rutland@....com
> Subject: Re: [PATCH] perf tool: arch: arm64: change the way for get_cpuid_str()
> function
>
> 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.
Hi Will,
tools/perf/utils/metricgroup.c:
metricgroup__add_metric()/metricgroup__has_metric()/metricgroup__print()---->perf_pmu__find_map(NULL)------>perf_pmu__getcpuid(NULL)----->get_cpuid_str(NULL)
So, it will eventually pass NULL to get_cpuid_str() function for arm64, and now get_cpuid_str() for arm64 need *struct perf_pmu* entity to return MIDR string.
And the declaration for get_cpuid_str() is char *get_cpuid_str(struct perf_pmu *pmu __maybe_unused) in tools/perf/utils/header.h file.
So, it can return MIDR string without passing *struct perf_pmu* entity. Arch PowerPC/x86/s390 which implement metricgroup all add __maybe_unused.
> > 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.
The implement of get_cpuid_str() for arm64 now only can return the MIDR string of the first online cpu. I think it is also broken for heterogeneous systems.
Will, do you know how to fix this issue more reasonable?
Best Regards,
Joakim Zhang
> 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
> >
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