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Linus Torvalds 6ac40ed041 x86: quick TSC calibration 
Introduce a fast TSC-calibration method on sane hardware.

It only uses 17920 PIT timer ticks to calibrate the TSC, plus 256 ticks on
each side to make sure the TSC values were very close to the tick, so the
whole calibration takes 15ms. Yet, despite only takign 15ms,
we can actually give pretty stringent guarantees of accuracy:

 - the code requires that we hit each 256-counter block at least 50 times,
   so the TSC error is basically at *MOST* just a few PIT cycles off in
   any direction. In practice, it's going to be about one microseconds
   off (which is how long it takes to read the counter)

 - so over 17920 PIT cycles, we can pretty much guarantee that the
   calibration error is less than one half of a percent.

My testing bears this out: on my machine, the quick-calibration reports
2934.085kHz, while the slow one reports 2933.415.

Yes, the slower calibration is still more precise. For me, the slow
calibration is stable to within about one hundreth of a percent, so it's
(at a guess) roughly an order-and-a-half of magnitude more precise. The
longer you wait, the more precise you can be.

However, the nice thing about the fast TSC PIT synchronization is that
it's pretty much _guaranteed_ to give that 0.5% precision, and fail
gracefully (and very quickly) if it doesn't get it. And it really is
fairly simple (even if there's a lot of _details_ there, and I didn't get
all of those right ont he first try or even the second ;)

The patch says "110 insertions", but 63 of those new lines are actually
comments.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 arch/x86/kernel/tsc.c |  111 ++++++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 110 insertions(+), 1 deletions(-)
2008-09-04 22:54:50 +02:00
..
acpi x86: fix i486 suspend to disk CR4 oops 2008-08-18 08:50:19 +02:00
cpu Merge branch 'linus' into x86/urgent 2008-08-25 14:39:12 +02:00
.gitignore arch/x86/kernel/.gitignore: Added vmlinux.lds to .gitignore file because it shouldn't be tracked. 2008-07-10 10:13:51 -07:00
alternative.c x86: fix SMP alternatives: use mutex instead of spinlock, text_poke is sleepable 2008-05-23 21:56:52 +02:00
amd_iommu.c x86 iommu: remove unneeded parenthesis 2008-08-19 02:16:24 +02:00
amd_iommu_init.c x86, AMD IOMMU: initialize dma_ops after sysfs registration 2008-08-15 13:56:56 +02:00
aperture_64.c x86: make only GART code include gart.h 2008-07-11 11:00:54 +02:00
apic_32.c x86: resurrect proper handling of maxcpus= kernel option (v2) 2008-08-14 11:18:08 +02:00
apic_64.c x86: resurrect proper handling of maxcpus= kernel option (v2) 2008-08-14 11:18:08 +02:00
apm_32.c remove include/linux/pm_legacy.h 2008-07-24 10:47:22 -07:00
asm-offsets.c
asm-offsets_32.c x86/paravirt: split sysret and sysexit 2008-07-08 13:13:15 +02:00
asm-offsets_64.c xen64: add asm-offsets 2008-07-16 10:58:55 +02:00
audit_64.c
bios_uv.c x86 BIOS interface for RTC on SGI UV 2008-07-18 14:35:14 +02:00
bootflag.c
cpuid.c x86: cpuid: correct return value on partial operations 2008-08-25 17:46:12 -07:00
crash.c x86: allow machine_crash_shutdown to be replaced 2008-04-27 12:00:29 +03:00
crash_dump_32.c
crash_dump_64.c
doublefault_32.c
ds.c x86: debug Store - call kfree if only we really need it 2008-04-17 17:41:34 +02:00
e820.c x86: introduce x86_quirks 2008-07-20 09:18:17 +02:00
early-quirks.c Merge branches 'x86/urgent', 'x86/amd-iommu', 'x86/apic', 'x86/cleanups', 'x86/core', 'x86/cpu', 'x86/fixmap', 'x86/gart', 'x86/kprobes', 'x86/memtest', 'x86/modules', 'x86/nmi', 'x86/pat', 'x86/reboot', 'x86/setup', 'x86/step', 'x86/unify-pci', 'x86/uv', 'x86/xen' and 'xen-64bit' into x86/for-linus 2008-07-21 16:37:17 +02:00
early_printk.c x86, generic: mark early_printk as asmlinkage 2008-06-18 13:11:01 +02:00
efi.c x86: introduce max_low_pfn_mapped for 64-bit 2008-07-11 10:24:04 +02:00
efi_32.c x86: fix i486 suspend to disk CR4 oops 2008-08-18 08:50:19 +02:00
efi_64.c x86: add flags parameter to reserve_bootmem_generic() 2008-07-08 11:49:49 +02:00
efi_stub_32.S
efi_stub_64.S
entry_32.S i386 syscall audit fast-path 2008-07-23 18:00:30 -07:00
entry_64.S x86_64 ia32 syscall audit fast-path 2008-07-23 17:55:22 -07:00
ftrace.c ftrace: store mcount address in rec->ip 2008-06-23 22:10:56 +02:00
genapic_64.c GRU Driver: export is_uv_system(), zap_page_range() & follow_page() 2008-07-30 09:41:48 -07:00
genapic_flat_64.c NR_CPUS: Replace NR_CPUS in arch/x86/kernel/genapic_flat_64.c 2008-07-20 10:21:10 +02:00
genx2apic_uv_x.c x86: fix section mismatch warning - uv_cpu_init 2008-08-22 14:12:20 +02:00
geode_32.c x86, geode: add a VSA2 ID for General Software 2008-06-19 14:19:03 +02:00
head.c x86: move reserve_setup_data to setup.c 2008-07-08 13:16:14 +02:00
head32.c x86: extract common part of head32.c and head64.c into head.c 2008-06-05 15:10:02 +02:00
head64.c x86-64: fix overlap of modules and fixmap areas 2008-08-15 17:31:50 +02:00
head_32.S x86: fix cpu hotplug on 32bit 2008-07-27 21:43:11 +02:00
head_64.S Revert "x86_64: there's no need to preallocate level1_fixmap_pgt" 2008-07-16 11:07:30 +02:00
hpet.c x86: hpet: workaround SB700 BIOS 2008-08-14 13:23:45 +02:00
i386_ksyms_32.c ftrace: store mcount address in rec->ip 2008-06-23 22:10:56 +02:00
i387.c x86 ptrace: fix PTRACE_GETFPXREGS error 2008-07-01 11:03:31 +02:00
i8237.c
i8253.c x86: cleanup div_sc() usage 2008-04-26 17:35:47 +02:00
i8259.c i8259: fix final ugliness 2008-06-02 11:55:52 +02:00
init_task.c [PATCH] take init_files to fs/file.c 2008-05-16 17:22:20 -04:00
io_apic_32.c x86: Restore proper vector locking during cpu hotplug 2008-08-11 10:37:34 +02:00
io_apic_64.c x86: Restore proper vector locking during cpu hotplug 2008-08-11 10:37:34 +02:00
io_delay.c x86: io delay - add checking for NULL early param 2008-07-09 13:57:54 +02:00
ioport.c
ipi.c x86: APIC: remove apic_write_around(); use alternatives 2008-07-18 12:51:21 +02:00
irq_32.c x86: use __page_aligned_data/bss 2008-07-16 10:54:39 +02:00
irq_64.c x86: make /proc/stat account for all interrupts 2008-05-25 07:11:49 +02:00
irqinit_32.c x86: rename the i8259_32/64.c leftovers to irqinit_32/64.c 2008-05-24 16:47:39 +02:00
irqinit_64.c x86-64: make BUILD_IRQ() also reset section back 2008-07-24 12:49:26 -07:00
k8.c
kdebugfs.c x86: Add a arch directory for x86 under debugfs 2008-07-18 17:22:04 -07:00
kgdb.c x86: KGDB build fix 2008-04-19 19:19:54 +02:00
kprobes.c kprobes: improve kretprobe scalability with hashed locking 2008-07-25 10:53:30 -07:00
kvm.c x86: KVM guest: hypercall batching 2008-04-27 12:00:28 +03:00
kvmclock.c x86: KVM guest: make kvm_smp_prepare_boot_cpu() static 2008-07-20 12:42:37 +03:00
ldt.c cpumask: change cpumask_of_cpu_ptr to use new cpumask_of_cpu 2008-07-26 16:40:33 +02:00
machine_kexec_32.c kexec jump: fix for ftrace 2008-08-15 08:35:43 -07:00
machine_kexec_64.c kexec jump 2008-07-26 12:00:04 -07:00
Makefile Merge branch 'x86/paravirt-spinlocks' into x86/for-linus 2008-07-21 16:45:56 +02:00
mca_32.c
mfgpt_32.c x86, geode-mfgpt: check IRQ before using MFGPT as clocksource 2008-08-15 17:12:32 +02:00
microcode.c cpumask: change cpumask_of_cpu_ptr to use new cpumask_of_cpu 2008-07-26 16:40:33 +02:00
mmconf-fam10h_64.c x86: mmconf: fix section mismatch warning 2008-08-18 07:49:06 +02:00
module_32.c
module_64.c PAGE_ALIGN(): correctly handle 64-bit values on 32-bit architectures 2008-07-24 10:47:21 -07:00
mpparse.c x86: mpparse.c: fix section mismatch warning 2008-08-18 07:49:26 +02:00
msr.c x86: msr: correct return value on partial operations 2008-08-25 17:46:12 -07:00
nmi.c x86, nmi: clean UP NMI watchdog failure message 2008-08-15 15:35:31 +02:00
numaq_32.c x86: fix BUG: unable to handle kernel paging request (numaq_tsc_disable) 2008-08-21 12:52:01 +02:00
olpc.c x86: olpc: add One Laptop Per Child architecture support 2008-04-29 08:06:07 -07:00
paravirt.c x86: export pv_lock_ops non-GPL 2008-08-21 12:42:23 +02:00
paravirt_patch_32.c x86/paravirt: split sysret and sysexit 2008-07-08 13:13:15 +02:00
paravirt_patch_64.c x86/paravirt: add sysret/sysexit pvops for returning to 32-bit compatibility userspace 2008-07-08 13:15:52 +02:00
pci-calgary_64.c x86: use WARN() in arch/x86/kernel 2008-08-21 10:01:52 +02:00
pci-dma.c generic, x86: fix add iommu_num_pages helper function 2008-07-29 12:12:48 +02:00
pci-gart_64.c Merge branch 'x86/iommu' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip into for-linus 2008-07-28 14:31:10 -07:00
pci-nommu.c dma-mapping: add the device argument to dma_mapping_error() 2008-07-26 12:00:03 -07:00
pci-swiotlb_64.c dma-mapping: add the device argument to dma_mapping_error() 2008-07-26 12:00:03 -07:00
pcspeaker.c
pmtimer_64.c
probe_roms_32.c x86: seperate probe_roms into another file 2008-07-08 12:50:05 +02:00
process.c Merge branches 'x86/urgent', 'x86/amd-iommu', 'x86/apic', 'x86/cleanups', 'x86/core', 'x86/cpu', 'x86/fixmap', 'x86/gart', 'x86/kprobes', 'x86/memtest', 'x86/modules', 'x86/nmi', 'x86/pat', 'x86/reboot', 'x86/setup', 'x86/step', 'x86/unify-pci', 'x86/uv', 'x86/xen' and 'xen-64bit' into x86/for-linus 2008-07-21 16:37:17 +02:00
process_32.c x86: invalidate caches before going into suspend 2008-08-15 14:04:30 +02:00
process_64.c x86: invalidate caches before going into suspend 2008-08-15 14:04:30 +02:00
ptrace.c x86 ptrace: user-sets-TF nits 2008-07-16 12:15:17 -07:00
pvclock.c x86: Add structs and functions for paravirt clocksource 2008-06-24 21:02:31 +03:00
quirks.c Merge branch 'timers/for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2008-07-15 10:39:57 -07:00
reboot.c cpumask: change cpumask_of_cpu_ptr to use new cpumask_of_cpu 2008-07-26 16:40:33 +02:00
reboot_fixups_32.c x86: constify data in reboot.c 2008-05-25 08:58:30 +02:00
relocate_kernel_32.S kexec jump: check code size in control page 2008-08-15 08:35:42 -07:00
relocate_kernel_64.S
rtc.c provide rtc_cmos platform device 2008-06-12 18:05:42 -07:00
scx200_32.c
setup.c x86: fix VMI for early params 2008-08-22 08:01:54 +02:00
setup_percpu.c cpu masks: optimize and clean up cpumask_of_cpu() 2008-07-28 22:20:41 +02:00
sigframe.h
signal_32.c Merge branch 'sched/for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2008-07-23 19:36:53 -07:00
signal_64.c x64, fpu: fix possible FPU leakage in error conditions 2008-07-26 16:37:04 +02:00
smp.c generic-ipi: fixlet 2008-07-06 14:01:50 +02:00
smpboot.c x86: fix section mismatch warning - uv_cpu_init 2008-08-22 14:12:20 +02:00
smpcommon.c x86: change init_gdt to update the gdt via write_gdt, rather than a direct write. 2008-08-15 19:16:05 +02:00
stacktrace.c stacktrace: fix modular build, export print_stack_trace and save_stack_trace 2008-06-30 09:20:55 +02:00
step.c x86 ptrace: user-sets-TF nits 2008-07-16 12:15:17 -07:00
summit_32.c x86: make generic arch support NUMAQ 2008-06-10 11:34:42 +02:00
sys_i386_32.c x86: coding style fixes to arch/x86/kernel/sys_i386_32.c 2008-06-10 12:34:54 +02:00
sys_x86_64.c unified (weak) sys_pipe implementation 2008-05-03 13:50:33 -07:00
syscall_64.c
syscall_table_32.S flag parameters add-on: remove epoll_create size param 2008-07-24 10:47:29 -07:00
tce_64.c
test_nx.c
test_rodata.c
time_32.c x86: add ->pre_time_init to x86_quirks 2008-07-20 09:25:52 +02:00
time_64.c x86: merge tsc_init and clocksource code 2008-07-09 07:43:27 +02:00
tlb_32.c on_each_cpu(): kill unused 'retry' parameter 2008-06-26 11:24:38 +02:00
tlb_64.c Merge branch 'generic-ipi' into generic-ipi-for-linus 2008-07-15 21:55:59 +02:00
tlb_uv.c x86, SGI UV: hardcode the TLB flush interrupt system vector 2008-08-20 12:36:03 +02:00
tls.c
tls.h
topology.c
trampoline.c x86: extend e820 ealy_res support 32bit 2008-05-25 10:55:11 +02:00
trampoline_32.S x86: trampoline_32.S - switch to .cpuinit.data 2008-04-26 17:35:47 +02:00
trampoline_64.S x86: move suspend wakeup code to C 2008-04-17 17:41:37 +02:00
traps_32.c x86: introducing asm-x86/traps.h 2008-07-18 18:51:57 +02:00
traps_64.c x64, fpu: fix possible FPU leakage in error conditions 2008-07-26 16:37:04 +02:00
tsc.c x86: quick TSC calibration 2008-09-04 22:54:50 +02:00
tsc_sync.c x86: use WARN() in arch/x86/kernel 2008-08-21 10:01:52 +02:00
verify_cpu_64.S
visws_quirks.c x86: resurrect proper handling of maxcpus= kernel option (v2) 2008-08-14 11:18:08 +02:00
vm86_32.c x86: replace most VM86 flags with flags from processor-flags.h 2008-04-17 17:41:33 +02:00
vmi_32.c x86: Fix broken VMI in 2.6.27-rc.. 2008-08-08 15:22:02 -07:00
vmiclock_32.c x86: rename paravirtualized TSC functions 2008-07-09 07:43:28 +02:00
vmlinux.lds.S
vmlinux_32.lds.S kexec jump: check code size in control page 2008-08-15 08:35:42 -07:00
vmlinux_64.lds.S Merge branch 'core/rodata' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2008-07-14 15:28:10 -07:00
vsmp_64.c x86: vsmp_64 add missing includes 2008-05-25 08:58:24 +02:00
vsyscall_64.c Merge branch 'generic-ipi' into generic-ipi-for-linus 2008-07-15 21:55:59 +02:00
x8664_ksyms_64.c Merge branch 'auto-ftrace-next' into tracing/for-linus 2008-07-14 16:11:52 +02:00