Add detect_art() call to early TSC initialization which reads ART->TSC
numerator/denominator and sets CPU feature if present
Add convert_art_to_tsc() function performing conversion ART to TSC
Add art_timestamp referencing art_to_tsc() and clocksource_tsc enabling
driver conversion of ART to TSC
Signed-off-by: Christopher S. Hall <christopher.s.h...@intel.com>
---
arch/x86/include/asm/cpufeature.h | 3 ++-
arch/x86/include/asm/tsc.h | 2 ++
arch/x86/kernel/tsc.c | 54 +++++++++++++++++++++++++++++++++++++++
3 files changed, 58 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/cpufeature.h
b/arch/x86/include/asm/cpufeature.h
index 3d6606f..a9322e5 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -85,7 +85,7 @@
#define X86_FEATURE_P4 ( 3*32+ 7) /* "" P4 */
#define X86_FEATURE_CONSTANT_TSC ( 3*32+ 8) /* TSC ticks at a constant rate */
#define X86_FEATURE_UP ( 3*32+ 9) /* smp kernel running on up */
-/* free, was #define X86_FEATURE_FXSAVE_LEAK ( 3*32+10) * "" FXSAVE leaks
FOP/FIP/FOP */
+#define X86_FEATURE_ART (3*32+10) /* Platform has always
running timer (ART) */
#define X86_FEATURE_ARCH_PERFMON ( 3*32+11) /* Intel Architectural PerfMon */
#define X86_FEATURE_PEBS ( 3*32+12) /* Precise-Event Based Sampling */
#define X86_FEATURE_BTS ( 3*32+13) /* Branch Trace Store */
@@ -352,6 +352,7 @@ extern const char * const x86_bug_flags[NBUGINTS*32];
#define cpu_has_de boot_cpu_has(X86_FEATURE_DE)
#define cpu_has_pse boot_cpu_has(X86_FEATURE_PSE)
#define cpu_has_tsc boot_cpu_has(X86_FEATURE_TSC)
+#define cpu_has_art boot_cpu_has(X86_FEATURE_ART)
#define cpu_has_pge boot_cpu_has(X86_FEATURE_PGE)
#define cpu_has_apic boot_cpu_has(X86_FEATURE_APIC)
#define cpu_has_sep boot_cpu_has(X86_FEATURE_SEP)
diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
index 94605c0..8d52d91 100644
--- a/arch/x86/include/asm/tsc.h
+++ b/arch/x86/include/asm/tsc.h
@@ -45,6 +45,8 @@ static __always_inline cycles_t vget_cycles(void)
return (cycles_t)__native_read_tsc();
}
+extern struct correlated_cs art_timestamper;
+
extern void tsc_init(void);
extern void mark_tsc_unstable(char *reason);
extern int unsynchronized_tsc(void);
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 7437b41..13f12e0 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -939,10 +939,36 @@ static struct notifier_block time_cpufreq_notifier_block
= {
.notifier_call = time_cpufreq_notifier
};
+#define ART_CPUID_LEAF (0x15)
+#define ART_MIN_DENOMINATOR (2)
+
+static u32 art_to_tsc_numerator;
+static u32 art_to_tsc_denominator;
+
+/*
+ * If ART is present detect the numberator:denominator to convert to TSC
+ */
+void detect_art(void)
+{
+ unsigned int unused[2];
+
+ if (boot_cpu_data.cpuid_level >= ART_CPUID_LEAF) {
+ cpuid(ART_CPUID_LEAF, &art_to_tsc_denominator,
+ &art_to_tsc_numerator, unused, unused+1);
+
+ if (art_to_tsc_denominator >= ART_MIN_DENOMINATOR) {
+ set_cpu_cap(&boot_cpu_data, X86_FEATURE_ART);
+ }
+ }
+}
+
static int __init cpufreq_tsc(void)
{
if (!cpu_has_tsc)
return 0;
+
+ detect_art();
+
if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
return 0;
cpufreq_register_notifier(&time_cpufreq_notifier_block,
@@ -1059,6 +1085,32 @@ int unsynchronized_tsc(void)
return 0;
}
+/*
+ * Convert ART to TSC given numerator/denominator found in detect_art()
+ */
+static u64 convert_art_to_tsc(struct correlated_cs *cs, u64 cycles)
+{
+ u64 tmp, res;
+
+ switch (art_to_tsc_denominator) {
+ default:
+ res = (cycles / art_to_tsc_denominator) * art_to_tsc_numerator;
+ tmp = (cycles % art_to_tsc_denominator) * art_to_tsc_numerator;
+ res += tmp / art_to_tsc_denominator;
+ break;
+ case 2:
+ res = (cycles >> 1) * art_to_tsc_numerator;
+ tmp = (cycles & 0x1) * art_to_tsc_numerator;
+ res += tmp >> 1;
+ break;
+ }
+ return res;
+}
+
+struct correlated_cs art_timestamper = {
+ .convert = convert_art_to_tsc,
+};
+EXPORT_SYMBOL(art_timestamper);
static void tsc_refine_calibration_work(struct work_struct *work);
static DECLARE_DELAYED_WORK(tsc_irqwork, tsc_refine_calibration_work);
@@ -1130,6 +1182,8 @@ static void tsc_refine_calibration_work(struct
work_struct *work)
(unsigned long)tsc_khz % 1000);
out:
+ if (cpu_has_art)
+ art_timestamper.related_cs = &clocksource_tsc;
clocksource_register_khz(&clocksource_tsc, tsc_khz);
}
--
2.1.4
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