linux-kernel - Re: [PATCH v0 2/3] perf/x86/intel/pt: Export cpu frequency ratios needed by PT decoders

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Date:	Thu, 28 Apr 2016 18:55:49 +0300
From:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
	linux-kernel@...r.kernel.org, vince@...ter.net, eranian@...gle.com,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Mathieu Poirier <mathieu.poirier@...aro.org>
Subject: Re: [PATCH v0 2/3] perf/x86/intel/pt: Export cpu frequency ratios needed by PT decoders

Alexander Shishkin <alexander.shishkin@...ux.intel.com> writes:

> In order for Intel PT decoders to infer correct crystal clock and bus
> frequencies that are required to correctly decode timing information
> from a PT stream (MTC and CBR packets), export them as sysfs attributes:
>
>   * max_nonturbo_ratio: ratio between the invariant TSC and base clock;
>   * tsc_art_ratio: TSC to core crystal clock ratio.
>
> Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>

With a slightly better changelog:

>From d0fbc4e45fb633e464cbbd61d6aacd5a476fd50d Mon Sep 17 00:00:00 2001
From: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Date: Wed, 19 Aug 2015 17:02:10 +0300
Subject: [PATCH] perf/x86/intel/pt: Export cpu frequency ratios needed by PT
 decoders

Intel PT decoders need access to various bits of timing related
information to be able to correctly decode timing packets from a PT
stream (MTC and CBR packets). This patch exports all the necessary
bits as sysfs attributes for the sake of consistency:

  * max_nonturbo_ratio: ratio between the invariant TSC and base clock;
  * tsc_art_ratio: TSC to core crystal clock ratio (also available as
    CPUID.15H).

Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
---
 arch/x86/events/intel/pt.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++
 arch/x86/events/intel/pt.h |  6 ++++++
 2 files changed, 60 insertions(+)

diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c
index e88915ff98..bf0b0fe33d 100644
--- a/arch/x86/events/intel/pt.c
+++ b/arch/x86/events/intel/pt.c
@@ -125,9 +125,46 @@ static struct attribute_group pt_format_group = {
 	.attrs	= pt_formats_attr,
 };
 
+static ssize_t
+pt_timing_attr_show(struct device *dev, struct device_attribute *attr,
+		    char *page)
+{
+	struct perf_pmu_events_attr *pmu_attr =
+		container_of(attr, struct perf_pmu_events_attr, attr);
+
+	switch (pmu_attr->id) {
+	case 0:
+		return sprintf(page, "%lu\n", pt_pmu.max_nonturbo_ratio);
+	case 1:
+		return sprintf(page, "%u:%u\n",
+			       pt_pmu.tsc_art_num,
+			       pt_pmu.tsc_art_den);
+	default:
+		break;
+	}
+
+	return -EINVAL;
+}
+
+PMU_EVENT_ATTR(max_nonturbo_ratio, timing_attr_max_nonturbo_ratio, 0,
+	       pt_timing_attr_show);
+PMU_EVENT_ATTR(tsc_art_ratio, timing_attr_tsc_art_ratio, 1,
+	       pt_timing_attr_show);
+
+static struct attribute *pt_timing_attr[] = {
+	&timing_attr_max_nonturbo_ratio.attr.attr,
+	&timing_attr_tsc_art_ratio.attr.attr,
+	NULL,
+};
+
+static struct attribute_group pt_timing_group = {
+	.attrs	= pt_timing_attr,
+};
+
 static const struct attribute_group *pt_attr_groups[] = {
 	&pt_cap_group,
 	&pt_format_group,
+	&pt_timing_group,
 	NULL,
 };
 
@@ -140,6 +177,23 @@ static int __init pt_pmu_hw_init(void)
 	int ret;
 	long i;
 
+	rdmsrl(MSR_PLATFORM_INFO, reg);
+	pt_pmu.max_nonturbo_ratio = (reg & 0xff00) >> 8;
+
+	/*
+	 * if available, read in TSC to core crystal clock ratio,
+	 * otherwise, zero for numerator stands for "not enumerated"
+	 * as per SDM
+	 */
+	if (boot_cpu_data.cpuid_level >= CPUID_TSC_LEAF) {
+		u32 eax, ebx, ecx, edx;
+
+		cpuid(CPUID_TSC_LEAF, &eax, &ebx, &ecx, &edx);
+
+		pt_pmu.tsc_art_num = ebx;
+		pt_pmu.tsc_art_den = eax;
+	}
+
 	if (boot_cpu_has(X86_FEATURE_VMX)) {
 		/*
 		 * Intel SDM, 36.5 "Tracing post-VMXON" says that
diff --git a/arch/x86/events/intel/pt.h b/arch/x86/events/intel/pt.h
index 3abb5f5ccc..e5385b1fa0 100644
--- a/arch/x86/events/intel/pt.h
+++ b/arch/x86/events/intel/pt.h
@@ -48,6 +48,9 @@ struct topa_entry {
 #define PT_CPUID_LEAVES		2
 #define PT_CPUID_REGS_NUM	4 /* number of regsters (eax, ebx, ecx, edx) */
 
+/* TSC to Core Crystal Clock Ratio */
+#define CPUID_TSC_LEAF		0x15
+
 enum pt_capabilities {
 	PT_CAP_max_subleaf = 0,
 	PT_CAP_cr3_filtering,
@@ -66,6 +69,9 @@ struct pt_pmu {
 	struct pmu		pmu;
 	u32			caps[PT_CPUID_REGS_NUM * PT_CPUID_LEAVES];
 	bool			vmx;
+	unsigned long		max_nonturbo_ratio;
+	unsigned int		tsc_art_num;
+	unsigned int		tsc_art_den;
 };
 
 /**
-- 
2.8.0.rc3