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 unsigned int tsc_khz;
  17 EXPORT_SYMBOL(tsc_khz);
  18
  19 static unsigned int cyc2ns_scale __read_mostly;
  20
  21 void set_cyc2ns_scale(unsigned long khz)
  22 {
  23         cyc2ns_scale = (NSEC_PER_MSEC << NS_SCALE) / khz;
  24 }
  25
  26 static unsigned long long cycles_2_ns(unsigned long long cyc)
  27 {
  28         return (cyc * cyc2ns_scale) >> NS_SCALE;
  29 }
  30
  31 unsigned long long sched_clock(void)
  32 {
  33         unsigned long a = 0;
  34
  35         /* Could do CPU core sync here. Opteron can execute rdtsc speculatively,
  36          * which means it is not completely exact and may not be monotonous
  37          * between CPUs. But the errors should be too small to matter for
  38          * scheduling purposes.
  39          */
  40
  41         rdtscll(a);
  42         return cycles_2_ns(a);
  43 }
  44
  45 static int tsc_unstable;
  46
  47 inline int check_tsc_unstable(void)
  48 {
  49         return tsc_unstable;
  50 }
  51 #ifdef CONFIG_CPU_FREQ
  52
  53 /* Frequency scaling support. Adjust the TSC based timer when the cpu frequency
  54  * changes.
  55  *
  56  * RED-PEN: On SMP we assume all CPUs run with the same frequency.  It's
  57  * not that important because current Opteron setups do not support
  58  * scaling on SMP anyroads.
  59  *
  60  * Should fix up last_tsc too. Currently gettimeofday in the
  61  * first tick after the change will be slightly wrong.
  62  */
  63
  64 #include <linux/workqueue.h>
  65
  66 static unsigned int cpufreq_delayed_issched = 0;
  67 static unsigned int cpufreq_init = 0;
  68 static struct work_struct cpufreq_delayed_get_work;
  69
  70 static void handle_cpufreq_delayed_get(struct work_struct *v)
  71 {
  72         unsigned int cpu;
  73         for_each_online_cpu(cpu) {
  74                 cpufreq_get(cpu);
  75         }
  76         cpufreq_delayed_issched = 0;
  77 }
  78
  79 static unsigned int  ref_freq = 0;
  80 static unsigned long loops_per_jiffy_ref = 0;
  81
  82 static unsigned long tsc_khz_ref = 0;
  83
  84 static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
  85                                  void *data)
  86 {
  87         struct cpufreq_freqs *freq = data;
  88         unsigned long *lpj, dummy;
  89
  90         if (cpu_has(&cpu_data[freq->cpu], X86_FEATURE_CONSTANT_TSC))
  91                 return 0;
  92
  93         lpj = &dummy;
  94         if (!(freq->flags & CPUFREQ_CONST_LOOPS))
  95 #ifdef CONFIG_SMP
  96                 lpj = &cpu_data[freq->cpu].loops_per_jiffy;
  97 #else
  98                 lpj = &boot_cpu_data.loops_per_jiffy;
  99 #endif
 100
 101         if (!ref_freq) {
 102                 ref_freq = freq->old;
 103                 loops_per_jiffy_ref = *lpj;
 104                 tsc_khz_ref = tsc_khz;
 105         }
 106         if ((val == CPUFREQ_PRECHANGE  && freq->old < freq->new) ||
 107                 (val == CPUFREQ_POSTCHANGE && freq->old > freq->new) ||
 108                 (val == CPUFREQ_RESUMECHANGE)) {
 109                 *lpj =
 110                 cpufreq_scale(loops_per_jiffy_ref, ref_freq, freq->new);
 111
 112                 tsc_khz = cpufreq_scale(tsc_khz_ref, ref_freq, freq->new);
 113                 if (!(freq->flags & CPUFREQ_CONST_LOOPS))
 114                         mark_tsc_unstable("cpufreq changes");
 115         }
 116
 117         set_cyc2ns_scale(tsc_khz_ref);
 118
 119         return 0;
 120 }
 121
 122 static struct notifier_block time_cpufreq_notifier_block = {
 123         .notifier_call  = time_cpufreq_notifier
 124 };
 125
 126 static int __init cpufreq_tsc(void)
 127 {
 128         INIT_WORK(&cpufreq_delayed_get_work, handle_cpufreq_delayed_get);
 129         if (!cpufreq_register_notifier(&time_cpufreq_notifier_block,
 130                                        CPUFREQ_TRANSITION_NOTIFIER))
 131                 cpufreq_init = 1;
 132         return 0;
 133 }
 134
 135 core_initcall(cpufreq_tsc);
 136
 137 #endif
 138
 139 static int tsc_unstable = 0;
 140
 141 /*
 142  * Make an educated guess if the TSC is trustworthy and synchronized
 143  * over all CPUs.
 144  */
 145 __cpuinit int unsynchronized_tsc(void)
 146 {
 147         if (tsc_unstable)
 148                 return 1;
 149
 150 #ifdef CONFIG_SMP
 151         if (apic_is_clustered_box())
 152                 return 1;
 153 #endif
 154         /* Most intel systems have synchronized TSCs except for
 155            multi node systems */
 156         if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) {
 157 #ifdef CONFIG_ACPI
 158                 /* But TSC doesn't tick in C3 so don't use it there */
 159                 if (acpi_gbl_FADT.header.length > 0 && acpi_gbl_FADT.C3latency < 1000)
 160                         return 1;
 161 #endif
 162                 return 0;
 163         }
 164
 165         /* Assume multi socket systems are not synchronized */
 166         return num_present_cpus() > 1;
 167 }
 168
 169 int __init notsc_setup(char *s)
 170 {
 171         notsc = 1;
 172         return 1;
 173 }
 174
 175 __setup("notsc", notsc_setup);
 176
 177
 178 /* clock source code: */
 179 static cycle_t read_tsc(void)
 180 {
 181         cycle_t ret = (cycle_t)get_cycles_sync();
 182         return ret;
 183 }
 184
 185 static cycle_t __vsyscall_fn vread_tsc(void)
 186 {
 187         cycle_t ret = (cycle_t)get_cycles_sync();
 188         return ret;
 189 }
 190
 191 static struct clocksource clocksource_tsc = {
 192         .name                   = "tsc",
 193         .rating                 = 300,
 194         .read                   = read_tsc,
 195         .mask                   = CLOCKSOURCE_MASK(64),
 196         .shift                  = 22,
 197         .flags                  = CLOCK_SOURCE_IS_CONTINUOUS |
 198                                   CLOCK_SOURCE_MUST_VERIFY,
 199         .vread                  = vread_tsc,
 200 };
 201
 202 void mark_tsc_unstable(char *reason)
 203 {
 204         if (!tsc_unstable) {
 205                 tsc_unstable = 1;
 206                 printk("Marking TSC unstable due to %s\n", reason);
 207                 /* Change only the rating, when not registered */
 208                 if (clocksource_tsc.mult)
 209                         clocksource_change_rating(&clocksource_tsc, 0);
 210                 else
 211                         clocksource_tsc.rating = 0;
 212         }
 213 }
 214 EXPORT_SYMBOL_GPL(mark_tsc_unstable);
 215
 216 void __init init_tsc_clocksource(void)
 217 {
 218         if (!notsc) {
 219                 clocksource_tsc.mult = clocksource_khz2mult(tsc_khz,
 220                                                         clocksource_tsc.shift);
 221                 if (check_tsc_unstable())
 222                         clocksource_tsc.rating = 0;
 223
 224                 clocksource_register(&clocksource_tsc);
 225         }
 226 }