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