From 539eb11e6e904f2cd4f62908cc5e44d724879721 Mon Sep 17 00:00:00 2001 From: john stultz Date: Mon, 26 Jun 2006 00:25:10 -0700 Subject: [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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/i386/kernel/tsc.c | 316 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 316 insertions(+) create mode 100644 arch/i386/kernel/tsc.c (limited to 'arch/i386/kernel/tsc.c') 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 +#include +#include +#include + +#include +#include + +#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 -- cgit v1.2.3