Commit d7a5a181 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge branch 'x86-tsc-for-linus' of git://

* 'x86-tsc-for-linus' of git://
  x86: Check tsc available/disabled in the delayed init function
  x86: Improve TSC calibration using a delayed workqueue
  x86: Make tsc=reliable override boot time stability checks
parents 4f00b901 a8760eca
......@@ -2461,12 +2461,13 @@ and is between 256 and 4096 characters. It is defined in the file
to facilitate early boot debugging.
See also Documentation/trace/events.txt
tsc= Disable clocksource-must-verify flag for TSC.
tsc= Disable clocksource stability checks for TSC.
Format: <string>
[x86] reliable: mark tsc clocksource as reliable, this
disables clocksource verification at runtime.
Used to enable high-resolution timer mode on older
hardware, and in virtualized environment.
disables clocksource verification at runtime, as well
as the stability checks done at bootup. Used to enable
high-resolution timer mode on older hardware, and in
virtualized environment.
[x86] noirqtime: Do not use TSC to do irq accounting.
Used to run time disable IRQ_TIME_ACCOUNTING on any
platforms where RDTSC is slow and this accounting
......@@ -872,6 +872,9 @@ __cpuinit int unsynchronized_tsc(void)
if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
return 0;
if (tsc_clocksource_reliable)
return 0;
* Intel systems are normally all synchronized.
* Exceptions must mark TSC as unstable:
......@@ -879,14 +882,92 @@ __cpuinit int unsynchronized_tsc(void)
if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) {
/* assume multi socket systems are not synchronized: */
if (num_possible_cpus() > 1)
tsc_unstable = 1;
return 1;
return tsc_unstable;
return 0;
static void tsc_refine_calibration_work(struct work_struct *work);
static DECLARE_DELAYED_WORK(tsc_irqwork, tsc_refine_calibration_work);
* tsc_refine_calibration_work - Further refine tsc freq calibration
* @work - ignored.
* This functions uses delayed work over a period of a
* second to further refine the TSC freq value. Since this is
* timer based, instead of loop based, we don't block the boot
* process while this longer calibration is done.
* If there are any calibration anomolies (too many SMIs, etc),
* or the refined calibration is off by 1% of the fast early
* calibration, we throw out the new calibration and use the
* early calibration.
static void tsc_refine_calibration_work(struct work_struct *work)
static u64 tsc_start = -1, ref_start;
static int hpet;
u64 tsc_stop, ref_stop, delta;
unsigned long freq;
/* Don't bother refining TSC on unstable systems */
if (check_tsc_unstable())
goto out;
* Since the work is started early in boot, we may be
* delayed the first time we expire. So set the workqueue
* again once we know timers are working.
if (tsc_start == -1) {
* Only set hpet once, to avoid mixing hardware
* if the hpet becomes enabled later.
hpet = is_hpet_enabled();
schedule_delayed_work(&tsc_irqwork, HZ);
tsc_start = tsc_read_refs(&ref_start, hpet);
tsc_stop = tsc_read_refs(&ref_stop, hpet);
/* hpet or pmtimer available ? */
if (!hpet && !ref_start && !ref_stop)
goto out;
/* Check, whether the sampling was disturbed by an SMI */
if (tsc_start == ULLONG_MAX || tsc_stop == ULLONG_MAX)
goto out;
delta = tsc_stop - tsc_start;
delta *= 1000000LL;
if (hpet)
freq = calc_hpet_ref(delta, ref_start, ref_stop);
freq = calc_pmtimer_ref(delta, ref_start, ref_stop);
/* Make sure we're within 1% */
if (abs(tsc_khz - freq) > tsc_khz/100)
goto out;
tsc_khz = freq;
printk(KERN_INFO "Refined TSC clocksource calibration: "
"%lu.%03lu MHz.\n", (unsigned long)tsc_khz / 1000,
(unsigned long)tsc_khz % 1000);
clocksource_register_khz(&clocksource_tsc, tsc_khz);
static void __init init_tsc_clocksource(void)
static int __init init_tsc_clocksource(void)
if (!cpu_has_tsc || tsc_disabled > 0)
return 0;
if (tsc_clocksource_reliable)
clocksource_tsc.flags &= ~CLOCK_SOURCE_MUST_VERIFY;
/* lower the rating if we already know its unstable: */
......@@ -894,8 +975,14 @@ static void __init init_tsc_clocksource(void)
clocksource_tsc.rating = 0;
clocksource_tsc.flags &= ~CLOCK_SOURCE_IS_CONTINUOUS;
clocksource_register_khz(&clocksource_tsc, tsc_khz);
schedule_delayed_work(&tsc_irqwork, 0);
return 0;
* We use device_initcall here, to ensure we run after the hpet
* is fully initialized, which may occur at fs_initcall time.
void __init tsc_init(void)
......@@ -949,6 +1036,5 @@ void __init tsc_init(void)
mark_tsc_unstable("TSCs unsynchronized");
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