arch/x86/kernel/tsc_64.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 static unsigned int  ref_freq;
  65 static unsigned long loops_per_jiffy_ref;
  66 static unsigned long tsc_khz_ref;
  67
  68 static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
  69                                  void *data)
  70 {
  71         struct cpufreq_freqs *freq = data;
  72         unsigned long *lpj, dummy;
  73
  74         if (cpu_has(&cpu_data[freq->cpu], X86_FEATURE_CONSTANT_TSC))
  75                 return 0;
  76
  77         lpj = &dummy;
  78         if (!(freq->flags & CPUFREQ_CONST_LOOPS))
  79 #ifdef CONFIG_SMP
  80                 lpj = &cpu_data[freq->cpu].loops_per_jiffy;
  81 #else
  82                 lpj = &boot_cpu_data.loops_per_jiffy;
  83 #endif
  84
  85         if (!ref_freq) {
  86                 ref_freq = freq->old;
  87                 loops_per_jiffy_ref = *lpj;
  88                 tsc_khz_ref = tsc_khz;
  89         }
  90         if ((val == CPUFREQ_PRECHANGE  && freq->old < freq->new) ||
  91                 (val == CPUFREQ_POSTCHANGE && freq->old > freq->new) ||
  92                 (val == CPUFREQ_RESUMECHANGE)) {
  93                 *lpj =
  94                 cpufreq_scale(loops_per_jiffy_ref, ref_freq, freq->new);
  95
  96                 tsc_khz = cpufreq_scale(tsc_khz_ref, ref_freq, freq->new);
  97                 if (!(freq->flags & CPUFREQ_CONST_LOOPS))
  98                         mark_tsc_unstable("cpufreq changes");
  99         }
 100
 101         set_cyc2ns_scale(tsc_khz_ref);
 102
 103         return 0;
 104 }
 105
 106 static struct notifier_block time_cpufreq_notifier_block = {
 107         .notifier_call  = time_cpufreq_notifier
 108 };
 109
 110 static int __init cpufreq_tsc(void)
 111 {
 112         cpufreq_register_notifier(&time_cpufreq_notifier_block,
 113                                   CPUFREQ_TRANSITION_NOTIFIER);
 114         return 0;
 115 }
 116
 117 core_initcall(cpufreq_tsc);
 118
 119 #endif
 120
 121 /*
 122  * Make an educated guess if the TSC is trustworthy and synchronized
 123  * over all CPUs.
 124  */
 125 __cpuinit int unsynchronized_tsc(void)
 126 {
 127         if (tsc_unstable)
 128                 return 1;
 129
 130 #ifdef CONFIG_SMP
 131         if (apic_is_clustered_box())
 132                 return 1;
 133 #endif
 134         /* Most intel systems have synchronized TSCs except for
 135            multi node systems */
 136         if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) {
 137 #ifdef CONFIG_ACPI
 138                 /* But TSC doesn't tick in C3 so don't use it there */
 139                 if (acpi_gbl_FADT.header.length > 0 &&
 140                     acpi_gbl_FADT.C3latency < 1000)
 141                         return 1;
 142 #endif
 143                 return 0;
 144         }
 145
 146         /* Assume multi socket systems are not synchronized */
 147         return num_present_cpus() > 1;
 148 }
 149
 150 int __init notsc_setup(char *s)
 151 {
 152         notsc = 1;
 153         return 1;
 154 }
 155
 156 __setup("notsc", notsc_setup);
 157
 158
 159 /* clock source code: */
 160 static cycle_t read_tsc(void)
 161 {
 162         cycle_t ret = (cycle_t)get_cycles_sync();
 163         return ret;
 164 }
 165
 166 static cycle_t __vsyscall_fn vread_tsc(void)
 167 {
 168         cycle_t ret = (cycle_t)get_cycles_sync();
 169         return ret;
 170 }
 171
 172 static struct clocksource clocksource_tsc = {
 173         .name                   = "tsc",
 174         .rating                 = 300,
 175         .read                   = read_tsc,
 176         .mask                   = CLOCKSOURCE_MASK(64),
 177         .shift                  = 22,
 178         .flags                  = CLOCK_SOURCE_IS_CONTINUOUS |
 179                                   CLOCK_SOURCE_MUST_VERIFY,
 180         .vread                  = vread_tsc,
 181 };
 182
 183 void mark_tsc_unstable(char *reason)
 184 {
 185         if (!tsc_unstable) {
 186                 tsc_unstable = 1;
 187                 printk("Marking TSC unstable due to %s\n", reason);
 188                 /* Change only the rating, when not registered */
 189                 if (clocksource_tsc.mult)
 190                         clocksource_change_rating(&clocksource_tsc, 0);
 191                 else
 192                         clocksource_tsc.rating = 0;
 193         }
 194 }
 195 EXPORT_SYMBOL_GPL(mark_tsc_unstable);
 196
 197 void __init init_tsc_clocksource(void)
 198 {
 199         if (!notsc) {
 200                 clocksource_tsc.mult = clocksource_khz2mult(tsc_khz,
 201                                                         clocksource_tsc.shift);
 202                 if (check_tsc_unstable())
 203                         clocksource_tsc.rating = 0;
 204
 205                 clocksource_register(&clocksource_tsc);
 206         }
 207 }