diff options
Diffstat (limited to 'arch/x86/kernel/tsc_32.c')
| -rw-r--r-- | arch/x86/kernel/tsc_32.c | 46 |
1 files changed, 27 insertions, 19 deletions
diff --git a/arch/x86/kernel/tsc_32.c b/arch/x86/kernel/tsc_32.c index 43517e324be..e4790728b22 100644 --- a/arch/x86/kernel/tsc_32.c +++ b/arch/x86/kernel/tsc_32.c @@ -28,7 +28,8 @@ EXPORT_SYMBOL_GPL(tsc_khz); static int __init tsc_setup(char *str) { printk(KERN_WARNING "notsc: Kernel compiled with CONFIG_X86_TSC, " - "cannot disable TSC.\n"); + "cannot disable TSC completely.\n"); + mark_tsc_unstable("user disabled TSC"); return 1; } #else @@ -83,8 +84,8 @@ DEFINE_PER_CPU(unsigned long, cyc2ns); static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu) { - unsigned long flags, prev_scale, *scale; unsigned long long tsc_now, ns_now; + unsigned long flags, *scale; local_irq_save(flags); sched_clock_idle_sleep_event(); @@ -94,7 +95,6 @@ static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu) rdtscll(tsc_now); ns_now = __cycles_2_ns(tsc_now); - prev_scale = *scale; if (cpu_khz) *scale = (NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR)/cpu_khz; @@ -221,9 +221,9 @@ EXPORT_SYMBOL(recalibrate_cpu_khz); * 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 unsigned int ref_freq; +static unsigned long loops_per_jiffy_ref; +static unsigned long cpu_khz_ref; static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val, void *data) @@ -255,9 +255,7 @@ time_cpufreq_notifier(struct notifier_block *nb, unsigned long val, void *data) ref_freq, freq->new); if (!(freq->flags & CPUFREQ_CONST_LOOPS)) { tsc_khz = cpu_khz; - preempt_disable(); - set_cyc2ns_scale(cpu_khz, smp_processor_id()); - preempt_enable(); + set_cyc2ns_scale(cpu_khz, freq->cpu); /* * TSC based sched_clock turns * to junk w/ cpufreq @@ -285,15 +283,28 @@ core_initcall(cpufreq_tsc); /* clock source code */ -static unsigned long current_tsc_khz = 0; +static unsigned long current_tsc_khz; +static struct clocksource clocksource_tsc; +/* + * We compare the TSC to the cycle_last value in the clocksource + * structure to avoid a nasty time-warp issue. This can be observed in + * a very small window right after one CPU updated cycle_last under + * xtime lock and the other CPU reads a TSC value which is smaller + * than the cycle_last reference value due to a TSC which is slighty + * behind. This delta is nowhere else observable, but in that case it + * results in a forward time jump in the range of hours due to the + * unsigned delta calculation of the time keeping core code, which is + * necessary to support wrapping clocksources like pm timer. + */ static cycle_t read_tsc(void) { cycle_t ret; rdtscll(ret); - return ret; + return ret >= clocksource_tsc.cycle_last ? + ret : clocksource_tsc.cycle_last; } static struct clocksource clocksource_tsc = { @@ -393,13 +404,15 @@ void __init tsc_init(void) int cpu; if (!cpu_has_tsc) - goto out_no_tsc; + return; cpu_khz = calculate_cpu_khz(); tsc_khz = cpu_khz; - if (!cpu_khz) - goto out_no_tsc; + if (!cpu_khz) { + mark_tsc_unstable("could not calculate TSC khz"); + return; + } printk("Detected %lu.%03lu MHz processor.\n", (unsigned long)cpu_khz / 1000, @@ -432,9 +445,4 @@ void __init tsc_init(void) tsc_enabled = 1; clocksource_register(&clocksource_tsc); - - return; - -out_no_tsc: - setup_clear_cpu_cap(X86_FEATURE_TSC); } |