arch/x86_64/kernel/tsc.c

   1 #include <linux/kernel.h>
   2 #include <linux/sched.h>
   3 #include <linux/interrupt.h>
   4 #include <linux/init.h>
   5 #include <linux/clocksource.h>
   6 #include <linux/time.h>
   7 #include <linux/acpi.h>
   8 #include <linux/cpufreq.h>
   9
  10 #include <asm/timex.h>
  11
  12 static int notsc __initdata = 0;
  13
  14 unsigned int cpu_khz;           /* TSC clocks / usec, not used here */
  15 EXPORT_SYMBOL(cpu_khz);
  16
  17 static unsigned int cyc2ns_scale __read_mostly;
  18
  19 void set_cyc2ns_scale(unsigned long khz)
  20 {
  21         cyc2ns_scale = (NSEC_PER_MSEC << NS_SCALE) / khz;
  22 }
  23
  24 static unsigned long long cycles_2_ns(unsigned long long cyc)
  25 {
  26         return (cyc * cyc2ns_scale) >> NS_SCALE;
  27 }
  28
  29 unsigned long long sched_clock(void)
  30 {
  31         unsigned long a = 0;
  32
  33         /* Could do CPU core sync here. Opteron can execute rdtsc speculatively,
  34          * which means it is not completely exact and may not be monotonous
  35          * between CPUs. But the errors should be too small to matter for
  36          * scheduling purposes.
  37          */
  38
  39         rdtscll(a);
  40         return cycles_2_ns(a);
  41 }
  42
  43 static int tsc_unstable;
  44
  45 static inline int check_tsc_unstable(void)
  46 {
  47         return tsc_unstable;
  48 }
  49 #ifdef CONFIG_CPU_FREQ
  50
  51 /* Frequency scaling support. Adjust the TSC based timer when the cpu frequency
  52  * changes.
  53  *
  54  * RED-PEN: On SMP we assume all CPUs run with the same frequency.  It's
  55  * not that important because current Opteron setups do not support
  56  * scaling on SMP anyroads.
  57  *
  58  * Should fix up last_tsc too. Currently gettimeofday in the
  59  * first tick after the change will be slightly wrong.
  60  */
  61
  62 #include <linux/workqueue.h>
  63
  64 static unsigned int cpufreq_delayed_issched = 0;
  65 static unsigned int cpufreq_init = 0;
  66 static struct work_struct cpufreq_delayed_get_work;
  67
  68 static void handle_cpufreq_delayed_get(struct work_struct *v)
  69 {
  70         unsigned int cpu;
  71         for_each_online_cpu(cpu) {
  72                 cpufreq_get(cpu);
  73         }
  74         cpufreq_delayed_issched = 0;
  75 }
  76
  77 static unsigned int  ref_freq = 0;
  78 static unsigned long loops_per_jiffy_ref = 0;
  79
  80 static unsigned long cpu_khz_ref = 0;
  81
  82 static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
  83                                  void *data)
  84 {
  85         struct cpufreq_freqs *freq = data;
  86         unsigned long *lpj, dummy;
  87
  88         if (cpu_has(&cpu_data[freq->cpu], X86_FEATURE_CONSTANT_TSC))
  89                 return 0;
  90
  91         lpj = &dummy;
  92         if (!(freq->flags & CPUFREQ_CONST_LOOPS))
  93 #ifdef CONFIG_SMP
  94                 lpj = &cpu_data[freq->cpu].loops_per_jiffy;
  95 #else
  96                 lpj = &boot_cpu_data.loops_per_jiffy;
  97 #endif
  98
  99         if (!ref_freq) {
 100                 ref_freq = freq->old;
 101                 loops_per_jiffy_ref = *lpj;
 102                 cpu_khz_ref = cpu_khz;
 103         }
 104         if ((val == CPUFREQ_PRECHANGE  && freq->old < freq->new) ||
 105                 (val == CPUFREQ_POSTCHANGE && freq->old > freq->new) ||
 106                 (val == CPUFREQ_RESUMECHANGE)) {
 107                 *lpj =
 108                 cpufreq_scale(loops_per_jiffy_ref, ref_freq, freq->new);
 109
 110                 cpu_khz = cpufreq_scale(cpu_khz_ref, ref_freq, freq->new);
 111                 if (!(freq->flags & CPUFREQ_CONST_LOOPS))
 112                         mark_tsc_unstable();
 113         }
 114
 115         set_cyc2ns_scale(cpu_khz_ref);
 116
 117         return 0;
 118 }
 119
 120 static struct notifier_block time_cpufreq_notifier_block = {
 121         .notifier_call  = time_cpufreq_notifier
 122 };
 123
 124 static int __init cpufreq_tsc(void)
 125 {
 126         INIT_WORK(&cpufreq_delayed_get_work, handle_cpufreq_delayed_get);
 127         if (!cpufreq_register_notifier(&time_cpufreq_notifier_block,
 128                                        CPUFREQ_TRANSITION_NOTIFIER))
 129                 cpufreq_init = 1;
 130         return 0;
 131 }
 132
 133 core_initcall(cpufreq_tsc);
 134
 135 #endif
 136
 137 static int tsc_unstable = 0;
 138
 139 /*
 140  * Make an educated guess if the TSC is trustworthy and synchronized
 141  * over all CPUs.
 142  */
 143 __cpuinit int unsynchronized_tsc(void)
 144 {
 145         if (tsc_unstable)
 146                 return 1;
 147
 148 #ifdef CONFIG_SMP
 149         if (apic_is_clustered_box())
 150                 return 1;
 151 #endif
 152         /* Most intel systems have synchronized TSCs except for
 153            multi node systems */
 154         if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) {
 155 #ifdef CONFIG_ACPI
 156                 /* But TSC doesn't tick in C3 so don't use it there */
 157                 if (acpi_gbl_FADT.header.length > 0 && acpi_gbl_FADT.C3latency < 1000)
 158                         return 1;
 159 #endif
 160                 return 0;
 161         }
 162
 163         /* Assume multi socket systems are not synchronized */
 164         return num_present_cpus() > 1;
 165 }
 166
 167 int __init notsc_setup(char *s)
 168 {
 169         notsc = 1;
 170         return 1;
 171 }
 172
 173 __setup("notsc", notsc_setup);
 174
 175
 176 /* clock source code: */
 177 static cycle_t read_tsc(void)
 178 {
 179         cycle_t ret = (cycle_t)get_cycles_sync();
 180         return ret;
 181 }
 182
 183 static struct clocksource clocksource_tsc = {
 184         .name                   = "tsc",
 185         .rating                 = 300,
 186         .read                   = read_tsc,
 187         .mask                   = CLOCKSOURCE_MASK(64),
 188         .shift                  = 22,
 189         .flags                  = CLOCK_SOURCE_IS_CONTINUOUS |
 190                                   CLOCK_SOURCE_MUST_VERIFY,
 191 };
 192
 193 void mark_tsc_unstable(void)
 194 {
 195         if (!tsc_unstable) {
 196                 tsc_unstable = 1;
 197                 /* Change only the rating, when not registered */
 198                 if (clocksource_tsc.mult)
 199                         clocksource_change_rating(&clocksource_tsc, 0);
 200                 else
 201                         clocksource_tsc.rating = 0;
 202         }
 203 }
 204 EXPORT_SYMBOL_GPL(mark_tsc_unstable);
 205
 206 static int __init init_tsc_clocksource(void)
 207 {
 208         if (!notsc) {
 209                 clocksource_tsc.mult = clocksource_khz2mult(cpu_khz,
 210                                                         clocksource_tsc.shift);
 211                 if (check_tsc_unstable())
 212                         clocksource_tsc.rating = 0;
 213
 214                 return clocksource_register(&clocksource_tsc);
 215         }
 216         return 0;
 217 }
 218
 219 module_init(init_tsc_clocksource);