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Message-ID: <CAP-5=fUUG_A8723xAd=Z_6f-p7=+TrjQYEB1JVgB8weKyeRJAQ@mail.gmail.com>
Date: Mon, 18 Jul 2022 07:47:21 -0700
From: Ian Rogers <irogers@...gle.com>
To: "Liang, Kan" <kan.liang@...ux.intel.com>
Cc: perry.taylor@...el.com, caleb.biggers@...el.com,
kshipra.bopardikar@...el.com,
Zhengjun Xing <zhengjun.xing@...ux.intel.com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...hat.com>,
Namhyung Kim <namhyung@...nel.org>,
Maxime Coquelin <mcoquelin.stm32@...il.com>,
Alexandre Torgue <alexandre.torgue@...s.st.com>,
Andi Kleen <ak@...ux.intel.com>,
James Clark <james.clark@....com>,
John Garry <john.garry@...wei.com>,
linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH v3 2/2] perf tsc: Add arch TSC frequency information
On Mon, Jul 18, 2022 at 5:49 AM Liang, Kan <kan.liang@...ux.intel.com> wrote:
>
> On 2022-07-15 6:35 p.m., Ian Rogers wrote:
> > From: Kan Liang <kan.liang@...ux.intel.com>
> >
> > The TSC frequency information is required for the event metrics with
> > the literal, system_tsc_freq. For the newer Intel platform, the TSC
> > frequency information can be retrieved from the CPUID leaf 0x15.
> > If the TSC frequency information isn't present the /proc/cpuinfo
> > approach is used.
> >
> > Refactor cpuid for this use. Note, the previous stack pushing/popping
> > approach was broken on x86-64 that has stack red zones that would be
> > clobbered.
> >
> > Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
> > Signed-off-by: Ian Rogers <irogers@...gle.com>
> > ---
> > tools/perf/arch/x86/util/cpuid.h | 34 +++++++++++++++++++++++++++++++
> > tools/perf/arch/x86/util/header.c | 27 ++++++++++--------------
> > tools/perf/arch/x86/util/tsc.c | 33 ++++++++++++++++++++++++++++++
> > tools/perf/util/expr.c | 15 +++++++++++++-
> > tools/perf/util/tsc.h | 1 +
> > 5 files changed, 93 insertions(+), 17 deletions(-)
> > create mode 100644 tools/perf/arch/x86/util/cpuid.h
> >
> > diff --git a/tools/perf/arch/x86/util/cpuid.h b/tools/perf/arch/x86/util/cpuid.h
> > new file mode 100644
> > index 000000000000..0a3ae0ace7e9
> > --- /dev/null
> > +++ b/tools/perf/arch/x86/util/cpuid.h
> > @@ -0,0 +1,34 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#ifndef PERF_CPUID_H
> > +#define PERF_CPUID_H 1
> > +
> > +
> > +static inline void
> > +cpuid(unsigned int op, unsigned int op2, unsigned int *a, unsigned int *b,
> > + unsigned int *c, unsigned int *d)
> > +{
> > + /*
> > + * Preserve %ebx/%rbx register by either placing it in %rdi or saving it
> > + * on the stack - x86-64 needs to avoid the stack red zone. In PIC
> > + * compilations %ebx contains the address of the global offset
> > + * table. %rbx is occasionally used to address stack variables in
> > + * presence of dynamic allocas.
> > + */
> > + asm(
> > +#if defined(__x86_64__)
> > + "mov %%rbx, %%rdi\n"
> > + "cpuid\n"
> > + "xchg %%rdi, %%rbx\n"
> > +#else
> > + "pushl %%ebx\n"
> > + "cpuid\n"
> > + "movl %%ebx, %%edi\n"
> > + "popl %%ebx\n"
> > +#endif
> > + : "=a"(*a), "=D"(*b), "=c"(*c), "=d"(*d)
> > + : "a"(op), "2"(op2));
> > +}
> > +
> > +void get_cpuid_0(char *vendor, unsigned int *lvl);
> > +
> > +#endif
> > diff --git a/tools/perf/arch/x86/util/header.c b/tools/perf/arch/x86/util/header.c
> > index 578c8c568ffd..a51444a77a5f 100644
> > --- a/tools/perf/arch/x86/util/header.c
> > +++ b/tools/perf/arch/x86/util/header.c
> > @@ -9,18 +9,17 @@
> >
> > #include "../../../util/debug.h"
> > #include "../../../util/header.h"
> > +#include "cpuid.h"
> >
> > -static inline void
> > -cpuid(unsigned int op, unsigned int *a, unsigned int *b, unsigned int *c,
> > - unsigned int *d)
> > +void get_cpuid_0(char *vendor, unsigned int *lvl)
> > {
> > - __asm__ __volatile__ (".byte 0x53\n\tcpuid\n\t"
> > - "movl %%ebx, %%esi\n\t.byte 0x5b"
> > - : "=a" (*a),
> > - "=S" (*b),
> > - "=c" (*c),
> > - "=d" (*d)
> > - : "a" (op));
> > + unsigned int b, c, d;
> > +
> > + cpuid(0, 0, lvl, &b, &c, &d);
> > + strncpy(&vendor[0], (char *)(&b), 4);
> > + strncpy(&vendor[4], (char *)(&d), 4);
> > + strncpy(&vendor[8], (char *)(&c), 4);
> > + vendor[12] = '\0';
> > }
> >
> > static int
> > @@ -31,14 +30,10 @@ __get_cpuid(char *buffer, size_t sz, const char *fmt)
> > int nb;
> > char vendor[16];
> >
> > - cpuid(0, &lvl, &b, &c, &d);
> > - strncpy(&vendor[0], (char *)(&b), 4);
> > - strncpy(&vendor[4], (char *)(&d), 4);
> > - strncpy(&vendor[8], (char *)(&c), 4);
> > - vendor[12] = '\0';
> > + get_cpuid_0(vendor, &lvl);
> >
> > if (lvl >= 1) {
> > - cpuid(1, &a, &b, &c, &d);
> > + cpuid(1, 0, &a, &b, &c, &d);
> >
> > family = (a >> 8) & 0xf; /* bits 11 - 8 */
> > model = (a >> 4) & 0xf; /* Bits 7 - 4 */
> > diff --git a/tools/perf/arch/x86/util/tsc.c b/tools/perf/arch/x86/util/tsc.c
> > index 559365f8fe52..b69144f22489 100644
> > --- a/tools/perf/arch/x86/util/tsc.c
> > +++ b/tools/perf/arch/x86/util/tsc.c
> > @@ -1,7 +1,9 @@
> > // SPDX-License-Identifier: GPL-2.0
> > #include <linux/types.h>
> > +#include <string.h>
> >
> > #include "../../../util/tsc.h"
> > +#include "cpuid.h"
> >
> > u64 rdtsc(void)
> > {
> > @@ -11,3 +13,34 @@ u64 rdtsc(void)
> >
> > return low | ((u64)high) << 32;
> > }
> > +
> > +double arch_get_tsc_freq(void)
> > +{
> > + unsigned int a, b, c, d, lvl;
> > + static bool cached;
> > + static double tsc;
> > + char vendor[16];
> > +
> > + if (cached)
> > + return tsc;
> > +
> > + cached = true;
> > + get_cpuid_0(vendor, &lvl);
> > + if (!strstr(vendor, "Intel"))
> > + return 0;
> > +
> > + /*
> > + * Don't support Time Stamp Counter and
> > + * Nominal Core Crystal Clock Information Leaf.
> > + */
> > + if (lvl < 0x15)
> > + return 0;
> > +
> > + cpuid(0x15, 0, &a, &b, &c, &d);
> > + /* TSC frequency is not enumerated */
> > + if (!a || !b || !c)
> > + return 0;
> > +
> > + tsc = (double)c * (double)b / (double)a;
> > + return tsc;
> > +}
> > diff --git a/tools/perf/util/expr.c b/tools/perf/util/expr.c
> > index 4c81533e4b43..16f10e6d5ca5 100644
> > --- a/tools/perf/util/expr.c
> > +++ b/tools/perf/util/expr.c
> > @@ -12,6 +12,7 @@
> > #include "expr-bison.h"
> > #include "expr-flex.h"
> > #include "smt.h"
> > +#include "tsc.h"
> > #include <linux/err.h>
> > #include <linux/kernel.h>
> > #include <linux/zalloc.h>
> > @@ -443,9 +444,19 @@ static double system_tsc_freq(void)
> >
> > free(line);
> > fclose(cpuinfo);
> > + if (isnan(result))
> > + pr_err("Error reading system_tsc_freq");
> > +
> > return result;
> > }
> >
> > +#if !defined(__i386__) && !defined(__x86_64__)
> > +double arch_get_tsc_freq(void)
>
> Other arch_* functions are __weak functions. I think it's better to keep
> it consistent. It also avoid to add a new #if defined when adding a new
> arch. Is there a problem to use __weak here?
There are problems with weak in general and link time optimizations -
weak is implemented as a C compiler extension. There have been
patches/threads in the past about avoiding it. In this case it'd be
easy to get two arch_get_tsc_freq defined or none. Without weak these
are both linker errors. With weak your mileage varies.
Thanks,
Ian
> Thanks,
> Kan
>
> > +{
> > + return 0.0;
> > +}
> > +#endif
> > +
> > double expr__get_literal(const char *literal)
> > {
> > static struct cpu_topology *topology;
> > @@ -462,7 +473,9 @@ double expr__get_literal(const char *literal)
> > }
> >
> > if (!strcasecmp("#system_tsc_freq", literal)) {
> > - result = system_tsc_freq();
> > + result = arch_get_tsc_freq();
> > + if (fpclassify(result) == FP_ZERO)
> > + result = system_tsc_freq();
> > goto out;
> > }
> >
> > diff --git a/tools/perf/util/tsc.h b/tools/perf/util/tsc.h
> > index 7d83a31732a7..88fd1c4c1cb8 100644
> > --- a/tools/perf/util/tsc.h
> > +++ b/tools/perf/util/tsc.h
> > @@ -25,6 +25,7 @@ int perf_read_tsc_conversion(const struct perf_event_mmap_page *pc,
> > u64 perf_time_to_tsc(u64 ns, struct perf_tsc_conversion *tc);
> > u64 tsc_to_perf_time(u64 cyc, struct perf_tsc_conversion *tc);
> > u64 rdtsc(void);
> > +double arch_get_tsc_freq(void);
> >
> > size_t perf_event__fprintf_time_conv(union perf_event *event, FILE *fp);
> >
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