[PATCH] Time: i386 Conversion - part 2: Rework TSC Support

As part of the i386 conversion to the generic timekeeping infrastructure, this
introduces a new tsc.c file.  The code in this file replaces the TSC
initialization, management and access code currently in timer_tsc.c (which
will be removed) that we want to preserve.

The code also introduces the following functionality:

o tsc_khz: like cpu_khz but stores the TSC frequency on systems that do not
  change TSC frequency w/ CPU frequency

o check/mark_tsc_unstable: accessor/modifier flag for TSC timekeeping
  usability

o minor cleanups to calibration math.

This patch also includes a one line __cpuinitdata fix from Zwane Mwaikambo.

Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 316 insertions, 0 deletions

diff --git a/arch/i386/kernel/tsc.c b/arch/i386/kernel/tsc.c
new file mode 100644
index 000000000000..3b64eaafce2b
--- /dev/null
+++ b/arch/i386/kernel/tsc.c
@@ -0,0 +1,316 @@
+/*
+ * This code largely moved from arch/i386/kernel/timer/timer_tsc.c
+ * which was originally moved from arch/i386/kernel/time.c.
+ * See comments there for proper credits.
+ */
+
+#include <linux/workqueue.h>
+#include <linux/cpufreq.h>
+#include <linux/jiffies.h>
+#include <linux/init.h>
+
+#include <asm/tsc.h>
+#include <asm/io.h>
+
+#include "mach_timer.h"
+
+/*
+ * On some systems the TSC frequency does not
+ * change with the cpu frequency. So we need
+ * an extra value to store the TSC freq
+ */
+unsigned int tsc_khz;
+
+int tsc_disable __cpuinitdata = 0;
+
+#ifdef CONFIG_X86_TSC
+static int __init tsc_setup(char *str)
+{
+        printk(KERN_WARNING "notsc: Kernel compiled with CONFIG_X86_TSC, "
+                                "cannot disable TSC.\n");
+        return 1;
+}
+#else
+/*
+ * disable flag for tsc. Takes effect by clearing the TSC cpu flag
+ * in cpu/common.c
+ */
+static int __init tsc_setup(char *str)
+{
+        tsc_disable = 1;
+
+        return 1;
+}
+#endif
+
+__setup("notsc", tsc_setup);
+
+
+/*
+ * code to mark and check if the TSC is unstable
+ * due to cpufreq or due to unsynced TSCs
+ */
+static int tsc_unstable;
+
+static inline int check_tsc_unstable(void)
+{
+        return tsc_unstable;
+}
+
+void mark_tsc_unstable(void)
+{
+        tsc_unstable = 1;
+}
+EXPORT_SYMBOL_GPL(mark_tsc_unstable);
+
+/* Accellerators 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 percision, 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!"
+ */
+static unsigned long cyc2ns_scale __read_mostly;
+
+#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
+
+static inline void set_cyc2ns_scale(unsigned long cpu_khz)
+{
+        cyc2ns_scale = (1000000 << CYC2NS_SCALE_FACTOR)/cpu_khz;
+}
+
+static inline unsigned long long cycles_2_ns(unsigned long long cyc)
+{
+        return (cyc * cyc2ns_scale) >> CYC2NS_SCALE_FACTOR;
+}
+
+/*
+ * Scheduler clock - returns current time in nanosec units.
+ */
+unsigned long long sched_clock(void)
+{
+        unsigned long long this_offset;
+
+        /*
+         * in the NUMA case we dont use the TSC as they are not
+         * synchronized across all CPUs.
+         */
+#ifndef CONFIG_NUMA
+        if (!cpu_khz || check_tsc_unstable())
+#endif
+                /* no locking but a rare wrong value is not a big deal */
+                return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
+
+        /* read the Time Stamp Counter: */
+        rdtscll(this_offset);
+
+        /* return the value in ns */
+        return cycles_2_ns(this_offset);
+}
+
+static unsigned long calculate_cpu_khz(void)
+{
+        unsigned long long start, end;
+        unsigned long count;
+        u64 delta64;
+        int i;
+        unsigned long flags;
+
+        local_irq_save(flags);
+
+        /* run 3 times to ensure the cache is warm */
+        for (i = 0; i < 3; i++) {
+                mach_prepare_counter();
+                rdtscll(start);
+                mach_countup(&count);
+                rdtscll(end);
+        }
+        /*
+         * Error: ECTCNEVERSET
+         * The CTC wasn't reliable: we got a hit on the very first read,
+         * or the CPU was so fast/slow that the quotient wouldn't fit in
+         * 32 bits..
+         */
+        if (count <= 1)
+                goto err;
+
+        delta64 = end - start;
+
+        /* cpu freq too fast: */
+        if (delta64 > (1ULL<<32))
+                goto err;
+
+        /* cpu freq too slow: */
+        if (delta64 <= CALIBRATE_TIME_MSEC)
+                goto err;
+
+        delta64 += CALIBRATE_TIME_MSEC/2; /* round for do_div */
+        do_div(delta64,CALIBRATE_TIME_MSEC);
+
+        local_irq_restore(flags);
+        return (unsigned long)delta64;
+err:
+        local_irq_restore(flags);
+        return 0;
+}
+
+int recalibrate_cpu_khz(void)
+{
+#ifndef CONFIG_SMP
+        unsigned long cpu_khz_old = cpu_khz;
+
+        if (cpu_has_tsc) {
+                cpu_khz = calculate_cpu_khz();
+                tsc_khz = cpu_khz;
+                cpu_data[0].loops_per_jiffy =
+                        cpufreq_scale(cpu_data[0].loops_per_jiffy,
+                                        cpu_khz_old, cpu_khz);
+                return 0;
+        } else
+                return -ENODEV;
+#else
+        return -ENODEV;
+#endif
+}
+
+EXPORT_SYMBOL(recalibrate_cpu_khz);
+
+void tsc_init(void)
+{
+        if (!cpu_has_tsc || tsc_disable)
+                return;
+
+        cpu_khz = calculate_cpu_khz();
+        tsc_khz = cpu_khz;
+
+        if (!cpu_khz)
+                return;
+
+        printk("Detected %lu.%03lu MHz processor.\n",
+                                (unsigned long)cpu_khz / 1000,
+                                (unsigned long)cpu_khz % 1000);
+
+        set_cyc2ns_scale(cpu_khz);
+}
+
+#ifdef CONFIG_CPU_FREQ
+
+static unsigned int cpufreq_delayed_issched = 0;
+static unsigned int cpufreq_init = 0;
+static struct work_struct cpufreq_delayed_get_work;
+
+static void handle_cpufreq_delayed_get(void *v)
+{
+        unsigned int cpu;
+
+        for_each_online_cpu(cpu)
+                cpufreq_get(cpu);
+
+        cpufreq_delayed_issched = 0;
+}
+
+/*
+ * if we notice cpufreq oddness, schedule a call to cpufreq_get() as it tries
+ * to verify the CPU frequency the timing core thinks the CPU is running
+ * at is still correct.
+ */
+static inline void cpufreq_delayed_get(void)
+{
+        if (cpufreq_init && !cpufreq_delayed_issched) {
+                cpufreq_delayed_issched = 1;
+                printk(KERN_DEBUG "Checking if CPU frequency changed.\n");
+                schedule_work(&cpufreq_delayed_get_work);
+        }
+}
+
+/*
+ * if the CPU frequency is scaled, TSC-based delays will need a different
+ * loops_per_jiffy value to function properly.
+ */
+static unsigned int ref_freq = 0;
+static unsigned long loops_per_jiffy_ref = 0;
+static unsigned long cpu_khz_ref = 0;
+
+static int
+time_cpufreq_notifier(struct notifier_block *nb, unsigned long val, void *data)
+{
+        struct cpufreq_freqs *freq = data;
+
+        if (val != CPUFREQ_RESUMECHANGE && val != CPUFREQ_SUSPENDCHANGE)
+                write_seqlock_irq(&xtime_lock);
+
+        if (!ref_freq) {
+                if (!freq->old){
+                        ref_freq = freq->new;
+                        goto end;
+                }
+                ref_freq = freq->old;
+                loops_per_jiffy_ref = cpu_data[freq->cpu].loops_per_jiffy;
+                cpu_khz_ref = cpu_khz;
+        }
+
+        if ((val == CPUFREQ_PRECHANGE  && freq->old < freq->new) ||
+            (val == CPUFREQ_POSTCHANGE && freq->old > freq->new) ||
+            (val == CPUFREQ_RESUMECHANGE)) {
+                if (!(freq->flags & CPUFREQ_CONST_LOOPS))
+                        cpu_data[freq->cpu].loops_per_jiffy =
+                                cpufreq_scale(loops_per_jiffy_ref,
+                                                ref_freq, freq->new);
+
+                if (cpu_khz) {
+
+                        if (num_online_cpus() == 1)
+                                cpu_khz = cpufreq_scale(cpu_khz_ref,
+                                                ref_freq, freq->new);
+                        if (!(freq->flags & CPUFREQ_CONST_LOOPS)) {
+                                tsc_khz = cpu_khz;
+                                set_cyc2ns_scale(cpu_khz);
+                                /*
+                                 * TSC based sched_clock turns
+                                 * to junk w/ cpufreq
+                                 */
+                                mark_tsc_unstable();
+                        }
+                }
+        }
+end:
+        if (val != CPUFREQ_RESUMECHANGE && val != CPUFREQ_SUSPENDCHANGE)
+                write_sequnlock_irq(&xtime_lock);
+
+        return 0;
+}
+
+static struct notifier_block time_cpufreq_notifier_block = {
+        .notifier_call  = time_cpufreq_notifier
+};
+
+static int __init cpufreq_tsc(void)
+{
+        int ret;
+
+        INIT_WORK(&cpufreq_delayed_get_work, handle_cpufreq_delayed_get, NULL);
+        ret = cpufreq_register_notifier(&time_cpufreq_notifier_block,
+                                        CPUFREQ_TRANSITION_NOTIFIER);
+        if (!ret)
+                cpufreq_init = 1;
+
+        return ret;
+}
+
+core_initcall(cpufreq_tsc);
+
+#endif