From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Christopher S. Hall" Subject: [PATCH v8 6/8] x86: tsc: Always Running Timer (ART) correlated clocksource Date: Mon, 22 Feb 2016 03:15:24 -0800 Message-ID: <1456139726-3327-7-git-send-email-christopher.s.hall@intel.com> References: <1456139726-3327-1-git-send-email-christopher.s.hall@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: "Christopher S. Hall" , x86@kernel.org, linux-kernel@vger.kernel.org, intel-wired-lan@lists.osuosl.org, netdev@vger.kernel.org, kevin.b.stanton@intel.com, kevin.j.clarke@intel.com To: tglx@linutronix.de, richardcochran@gmail.com, mingo@redhat.com, john.stultz@linaro.org, hpa@zytor.com, jeffrey.t.kirsher@intel.com Return-path: In-Reply-To: <1456139726-3327-1-git-send-email-christopher.s.hall@intel.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On modern Intel systems TSC is derived from the new Always Running Time= r (ART). ART can be captured simultaneous to the capture of audio and network device clocks, allowing a correlation between timebas= es 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 =E2=80=9Cm=E2=80=9D and =E2=80=9Cn=E2=80=9D such that: TSC_value =3D (ART_value * m) / n + k [n >=3D 2] [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] Signed-off-by: Christopher S. Hall [jstultz: Tweaked to fix build issue, also reworked math for 64bit division on 32bit systems] Signed-off-by: John Stultz --- arch/x86/include/asm/cpufeature.h | 2 +- arch/x86/include/asm/tsc.h | 2 ++ arch/x86/kernel/tsc.c | 49 +++++++++++++++++++++++++++++++= ++++++++ 3 files changed, 52 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/c= pufeature.h index 7ad8c94..ff557b4 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 le= aks FOP/FIP/FOP */ +#define X86_FEATURE_ART (3*32+10) /* Platform has always running time= r (ART) */ #define X86_FEATURE_ARCH_PERFMON ( 3*32+11) /* Intel Architectural Per= fMon */ #define X86_FEATURE_PEBS ( 3*32+12) /* Precise-Event Based Sampling */ #define X86_FEATURE_BTS ( 3*32+13) /* Branch Trace Store */ diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h index 6d7c547..174c421 100644 --- a/arch/x86/include/asm/tsc.h +++ b/arch/x86/include/asm/tsc.h @@ -29,6 +29,8 @@ static inline cycles_t get_cycles(void) return rdtsc(); } =20 +extern struct system_counterval_t convert_art_to_tsc(cycle_t art); + 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 3d743da..3fa0f41 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -43,6 +43,10 @@ static DEFINE_STATIC_KEY_FALSE(__use_tsc); =20 int tsc_clocksource_reliable; =20 +static u32 art_to_tsc_numerator; +static u32 art_to_tsc_denominator; +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 obs= erves a @@ -949,10 +953,34 @@ static struct notifier_block time_cpufreq_notifie= r_block =3D { .notifier_call =3D time_cpufreq_notifier }; =20 +#define ART_CPUID_LEAF (0x15) +#define ART_MIN_DENOMINATOR (1) + + +/* + * If ART is present detect the numerator:denominator to convert to TS= C + */ +static void detect_art(void) +{ + unsigned int unused[2]; + + if (boot_cpu_data.cpuid_level >=3D ART_CPUID_LEAF) { + cpuid(ART_CPUID_LEAF, &art_to_tsc_denominator, + &art_to_tsc_numerator, unused, unused+1); + + if (boot_cpu_has(X86_FEATURE_NONSTOP_TSC) && + art_to_tsc_denominator >=3D 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, @@ -1071,6 +1099,25 @@ int unsynchronized_tsc(void) return 0; } =20 +/* + * 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 =3D do_div(art, art_to_tsc_denominator); + + res =3D art * art_to_tsc_numerator; + tmp =3D rem * art_to_tsc_numerator; + + do_div(tmp, art_to_tsc_denominator); + res +=3D tmp; + + return (struct system_counterval_t) {.cs =3D art_related_clocksource, + .cycles =3D res}; +} +EXPORT_SYMBOL(convert_art_to_tsc); =20 static void tsc_refine_calibration_work(struct work_struct *work); static DECLARE_DELAYED_WORK(tsc_irqwork, tsc_refine_calibration_work); @@ -1142,6 +1189,8 @@ static void tsc_refine_calibration_work(struct wo= rk_struct *work) (unsigned long)tsc_khz % 1000); =20 out: + if (boot_cpu_has(X86_FEATURE_ART)) + art_related_clocksource =3D &clocksource_tsc; clocksource_register_khz(&clocksource_tsc, tsc_khz); } =20 --=20 2.1.4