summaryrefslogtreecommitdiffstats
path: root/arch/x86/kernel/tsc.c
diff options
context:
space:
mode:
authorChristopher S. Hall <christopher.s.hall@intel.com>2016-02-29 06:33:47 -0800
committerJohn Stultz <john.stultz@linaro.org>2016-03-03 14:23:34 -0800
commitf9677e0f83080bb4186865868c359e72e1fac1ea (patch)
tree914a27f215d8c86f8ca60154c062a1281cffe677 /arch/x86/kernel/tsc.c
parent2c756feb18d9ec258dbb3a3d11c47e28820690d7 (diff)
downloadlinux-f9677e0f83080bb4186865868c359e72e1fac1ea.tar.bz2
x86/tsc: Always Running Timer (ART) correlated clocksource
On modern Intel systems TSC is derived from the new Always Running Timer (ART). ART can be captured simultaneous to the capture of audio and network device clocks, allowing a correlation between timebases to be constructed. Upon capture, the driver converts the captured ART value to the appropriate system clock using the correlated clocksource mechanism. On systems that support ART a new CPUID leaf (0x15) returns parameters “m” and “n” such that: TSC_value = (ART_value * m) / n + k [n >= 1] [k is an offset that can adjusted by a privileged agent. The IA32_TSC_ADJUST MSR is an example of an interface to adjust k. See 17.14.4 of the Intel SDM for more details] Cc: Prarit Bhargava <prarit@redhat.com> Cc: Richard Cochran <richardcochran@gmail.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@kernel.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: kevin.b.stanton@intel.com Cc: kevin.j.clarke@intel.com Cc: hpa@zytor.com Cc: jeffrey.t.kirsher@intel.com Cc: netdev@vger.kernel.org Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Christopher S. Hall <christopher.s.hall@intel.com> [jstultz: Tweaked to fix build issue, also reworked math for 64bit division on 32bit systems, as well as !CONFIG_CPU_FREQ build fixes] Signed-off-by: John Stultz <john.stultz@linaro.org>
Diffstat (limited to 'arch/x86/kernel/tsc.c')
-rw-r--r--arch/x86/kernel/tsc.c59
1 files changed, 59 insertions, 0 deletions
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 3d743da828d3..80d761e420c5 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -43,6 +43,11 @@ static DEFINE_STATIC_KEY_FALSE(__use_tsc);
int tsc_clocksource_reliable;
+static u32 art_to_tsc_numerator;
+static u32 art_to_tsc_denominator;
+static u64 art_to_tsc_offset;
+struct clocksource *art_related_clocksource;
+
/*
* Use a ring-buffer like data structure, where a writer advances the head by
* writing a new data entry and a reader advances the tail when it observes a
@@ -964,6 +969,37 @@ core_initcall(cpufreq_tsc);
#endif /* CONFIG_CPU_FREQ */
+#define ART_CPUID_LEAF (0x15)
+#define ART_MIN_DENOMINATOR (1)
+
+
+/*
+ * If ART is present detect the numerator:denominator to convert to TSC
+ */
+static void detect_art(void)
+{
+ unsigned int unused[2];
+
+ if (boot_cpu_data.cpuid_level < ART_CPUID_LEAF)
+ return;
+
+ cpuid(ART_CPUID_LEAF, &art_to_tsc_denominator,
+ &art_to_tsc_numerator, unused, unused+1);
+
+ /* Don't enable ART in a VM, non-stop TSC required */
+ if (boot_cpu_has(X86_FEATURE_HYPERVISOR) ||
+ !boot_cpu_has(X86_FEATURE_NONSTOP_TSC) ||
+ art_to_tsc_denominator < ART_MIN_DENOMINATOR)
+ return;
+
+ if (rdmsrl_safe(MSR_IA32_TSC_ADJUST, &art_to_tsc_offset))
+ return;
+
+ /* Make this sticky over multiple CPU init calls */
+ setup_force_cpu_cap(X86_FEATURE_ART);
+}
+
+
/* clocksource code */
static struct clocksource clocksource_tsc;
@@ -1071,6 +1107,25 @@ int unsynchronized_tsc(void)
return 0;
}
+/*
+ * Convert ART to TSC given numerator/denominator found in detect_art()
+ */
+struct system_counterval_t convert_art_to_tsc(cycle_t art)
+{
+ u64 tmp, res, rem;
+
+ rem = do_div(art, art_to_tsc_denominator);
+
+ res = art * art_to_tsc_numerator;
+ tmp = rem * art_to_tsc_numerator;
+
+ do_div(tmp, art_to_tsc_denominator);
+ res += tmp + art_to_tsc_offset;
+
+ return (struct system_counterval_t) {.cs = art_related_clocksource,
+ .cycles = res};
+}
+EXPORT_SYMBOL(convert_art_to_tsc);
static void tsc_refine_calibration_work(struct work_struct *work);
static DECLARE_DELAYED_WORK(tsc_irqwork, tsc_refine_calibration_work);
@@ -1142,6 +1197,8 @@ static void tsc_refine_calibration_work(struct work_struct *work)
(unsigned long)tsc_khz % 1000);
out:
+ if (boot_cpu_has(X86_FEATURE_ART))
+ art_related_clocksource = &clocksource_tsc;
clocksource_register_khz(&clocksource_tsc, tsc_khz);
}
@@ -1235,6 +1292,8 @@ void __init tsc_init(void)
mark_tsc_unstable("TSCs unsynchronized");
check_system_tsc_reliable();
+
+ detect_art();
}
#ifdef CONFIG_SMP