Re: [PATCH v3 2/2] perf tsc: Add arch TSC frequency information

["Liang, Kan" <kan.liang@linux.intel.com>]

On 2022-07-15 6:35 p.m., Ian Rogers wrote:
> From: Kan Liang <kan.liang@linux.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@linux.intel.com>
> Signed-off-by: Ian Rogers <irogers@google.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?

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);
>