1 files changed, 114 insertions, 0 deletions

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index e6ee14533c75..595f78a22212 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -4,6 +4,7 @@
 #include <linux/module.h>
 #include <linux/timer.h>
 #include <linux/acpi_pmtmr.h>
+#include <linux/cpufreq.h>
 
 #include <asm/hpet.h>
 
@@ -215,3 +216,116 @@ int recalibrate_cpu_khz(void)
 EXPORT_SYMBOL(recalibrate_cpu_khz);
 
 #endif /* CONFIG_X86_32 */
+
+/* Accelerators for sched_clock()
+ * convert from cycles(64bits) => nanoseconds (64bits)
+ *  basic equation:
+ *              ns = cycles / (freq / ns_per_sec)
+ *              ns = cycles * (ns_per_sec / freq)
+ *              ns = cycles * (10^9 / (cpu_khz * 10^3))
+ *              ns = cycles * (10^6 / cpu_khz)
+ *
+ *      Then we use scaling math (suggested by george@mvista.com) to get:
+ *              ns = cycles * (10^6 * SC / cpu_khz) / SC
+ *              ns = cycles * cyc2ns_scale / SC
+ *
+ *      And since SC is a constant power of two, we can convert the div
+ *  into a shift.
+ *
+ *  We can use khz divisor instead of mhz to keep a better precision, since
+ *  cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
+ *  (mathieu.desnoyers@polymtl.ca)
+ *
+ *                      -johnstul@us.ibm.com "math is hard, lets go shopping!"
+ */
+
+DEFINE_PER_CPU(unsigned long, cyc2ns);
+
+void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
+{
+        unsigned long long tsc_now, ns_now;
+        unsigned long flags, *scale;
+
+        local_irq_save(flags);
+        sched_clock_idle_sleep_event();
+
+        scale = &per_cpu(cyc2ns, cpu);
+
+        rdtscll(tsc_now);
+        ns_now = __cycles_2_ns(tsc_now);
+
+        if (cpu_khz)
+                *scale = (NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR)/cpu_khz;
+
+        sched_clock_idle_wakeup_event(0);
+        local_irq_restore(flags);
+}
+
+#ifdef CONFIG_CPU_FREQ
+
+/* Frequency scaling support. Adjust the TSC based timer when the cpu frequency
+ * changes.
+ *
+ * RED-PEN: On SMP we assume all CPUs run with the same frequency.  It's
+ * not that important because current Opteron setups do not support
+ * scaling on SMP anyroads.
+ *
+ * Should fix up last_tsc too. Currently gettimeofday in the
+ * first tick after the change will be slightly wrong.
+ */
+
+static unsigned int  ref_freq;
+static unsigned long loops_per_jiffy_ref;
+static unsigned long tsc_khz_ref;
+
+static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
+                                void *data)
+{
+        struct cpufreq_freqs *freq = data;
+        unsigned long *lpj, dummy;
+
+        if (cpu_has(&cpu_data(freq->cpu), X86_FEATURE_CONSTANT_TSC))
+                return 0;
+
+        lpj = &dummy;
+        if (!(freq->flags & CPUFREQ_CONST_LOOPS))
+#ifdef CONFIG_SMP
+                lpj = &cpu_data(freq->cpu).loops_per_jiffy;
+#else
+        lpj = &boot_cpu_data.loops_per_jiffy;
+#endif
+
+        if (!ref_freq) {
+                ref_freq = freq->old;
+                loops_per_jiffy_ref = *lpj;
+                tsc_khz_ref = tsc_khz;
+        }
+        if ((val == CPUFREQ_PRECHANGE  && freq->old < freq->new) ||
+                        (val == CPUFREQ_POSTCHANGE && freq->old > freq->new) ||
+                        (val == CPUFREQ_RESUMECHANGE)) {
+                *lpj =  cpufreq_scale(loops_per_jiffy_ref, ref_freq, freq->new);
+
+                tsc_khz = cpufreq_scale(tsc_khz_ref, ref_freq, freq->new);
+                if (!(freq->flags & CPUFREQ_CONST_LOOPS))
+                        mark_tsc_unstable("cpufreq changes");
+        }
+
+        set_cyc2ns_scale(tsc_khz_ref, freq->cpu);
+
+        return 0;
+}
+
+static struct notifier_block time_cpufreq_notifier_block = {
+        .notifier_call  = time_cpufreq_notifier
+};
+
+static int __init cpufreq_tsc(void)
+{
+        cpufreq_register_notifier(&time_cpufreq_notifier_block,
+                                CPUFREQ_TRANSITION_NOTIFIER);
+        return 0;
+}
+
+core_initcall(cpufreq_tsc);
+
+#endif /* CONFIG_CPU_FREQ */