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Thomas Gleixner 995bd3bb5c x86: Hpet: Avoid the comparator readback penalty 
Due to the overly intelligent design of HPETs, we need to workaround
the problem that the compare value which we write is already behind
the actual counter value at the point where the value hits the real
compare register. This happens for two reasons:

1) We read out the counter, add the delta and write the result to the
   compare register. When a NMI or SMI hits between the read out and
   the write then the counter can be ahead of the event already

2) The write to the compare register is delayed by up to two HPET
   cycles in certain chipsets.

We worked around this by reading back the compare register to make
sure that the written value has hit the hardware. For certain ICH9+
chipsets this can require two readouts, as the first one can return
the previous compare register value. That's bad performance wise for
the normal case where the event is far enough in the future.

As we already know that the write can be delayed by up to two cycles
we can avoid the read back of the compare register completely if we
make the decision whether the delta has elapsed already or not based
on the following calculation:

  cmp = event - actual_count;

If cmp is less than 8 HPET clock cycles, then we decide that the event
has happened already and return -ETIME. That covers the above #1 and
#2 problems which would cause a wait for HPET wraparound (~306
seconds).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Nix <nix@esperi.org.uk>
Tested-by: Artur Skawina <art.08.09@gmail.com>
Cc: Damien Wyart <damien.wyart@free.fr>
Tested-by: John Drescher <drescherjm@gmail.com>
Cc: Venkatesh Pallipadi <venki@google.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Andreas Herrmann <andreas.herrmann3@amd.com>
Tested-by: Borislav Petkov <borislav.petkov@amd.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
LKML-Reference: <alpine.LFD.2.00.1009151500060.2416@localhost6.localdomain6>
2010-09-18 12:09:13 +02:00
..
acpi Merge branch 'x86-asm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2010-08-06 10:07:34 -07:00
apic x86, UV: Fix initialization of max_pnode 2010-09-10 17:15:49 +02:00
cpu Merge branch 'x86-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2010-09-08 11:14:10 -07:00
.gitignore
alternative.c x86, alternatives: BUG on encountering an invalid CPU feature number 2010-07-13 14:57:50 -07:00
amd_iommu.c x86/amd-iommu: Export cache-coherency capability 2010-07-27 17:14:24 +02:00
amd_iommu_init.c x86/amd-iommu: Fall back to GART if initialization fails 2010-06-01 10:20:15 +02:00
apb_timer.c x86, mrst: add more timer config options 2010-05-19 13:45:39 -07:00
aperture_64.c x86, gcc-4.6: Fix set but not read variables 2010-07-20 15:38:30 -07:00
apm_32.c update email address 2010-07-19 10:56:54 +02:00
asm-offsets.c
asm-offsets_32.c
asm-offsets_64.c
audit_64.c
bios_uv.c Merge branch 'x86-uv-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2010-02-28 11:00:55 -08:00
bootflag.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
check.c
cpuid.c x86: convert cpu notifier to return encapsulate errno value 2010-05-27 09:12:48 -07:00
crash.c x86, UV: Make kdump avoid stack dumps 2010-07-21 11:33:27 -07:00
crash_dump_32.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
crash_dump_64.c
doublefault_32.c
dumpstack.c x86: Unify dumpstack.h and stacktrace.h 2010-06-08 23:29:52 +02:00
dumpstack_32.c x86: Unify dumpstack.h and stacktrace.h 2010-06-08 23:29:52 +02:00
dumpstack_64.c x86: Unify dumpstack.h and stacktrace.h 2010-06-08 23:29:52 +02:00
e820.c suspend: Move NVS save/restore code to generic suspend functionality 2010-06-10 11:02:34 -04:00
early-quirks.c x86: hpet: Work around hardware stupidity 2010-09-15 00:55:13 +02:00
early_printk.c earlyprintk,vga,kdb: Fix \b and \r for earlyprintk=vga with kdb 2010-05-20 21:04:31 -05:00
efi.c x86: Remove trailing spaces in messages 2010-02-07 17:47:51 +01:00
efi_32.c
efi_64.c
efi_stub_32.S
efi_stub_64.S
entry_32.S Merge branch 'x86-alternatives-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2010-08-06 16:24:17 -07:00
entry_64.S Mark arguments to certain syscalls as being const 2010-08-13 16:53:13 -07:00
ftrace.c Merge branch 'tracing/core' of git://git.kernel.org/pub/scm/linux/kernel/git/frederic/random-tracing into tracing/core 2010-02-27 10:06:10 +01:00
head.c
head32.c fix typos concerning "initiali[zs]e" 2010-06-16 18:05:05 +02:00
head64.c x86: Make sure free_init_pages() frees pages on page boundary 2010-03-29 18:55:33 +02:00
head_32.S x86-32: Separate 1:1 pagetables from swapper_pg_dir 2010-08-18 09:17:20 -07:00
head_64.S x86-64: Simplify loading initial_gs 2010-07-21 21:23:51 -07:00
hpet.c x86: Hpet: Avoid the comparator readback penalty 2010-09-18 12:09:13 +02:00
hw_breakpoint.c x86: Support for instruction breakpoints 2010-06-24 23:35:27 +02:00
i386_ksyms_32.c
i387.c Merge branch 'kvm-updates/2.6.36' of git://git.kernel.org/pub/scm/virt/kvm/kvm 2010-08-22 11:27:36 -07:00
i8237.c
i8253.c i8253: Convert i8253_lock to raw_spinlock 2010-03-02 10:28:38 +01:00
i8259.c x86, i8259: Only register sysdev if we have a real 8259 PIC 2010-07-20 15:27:33 -07:00
init_task.c Rename .data.cacheline_aligned to .data..cacheline_aligned. 2010-03-03 11:25:58 +01:00
io_delay.c
ioport.c x86-64, paravirt: Call set_iopl_mask() on 64 bits 2009-12-09 16:54:08 -08:00
irq.c genirq: Convert irq_desc.lock to raw_spinlock 2009-12-14 23:55:33 +01:00
irq_32.c
irq_64.c
irqinit.c x86: Merge simd_math_error() into math_error() 2010-05-03 13:39:29 -07:00
k8.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
kdebugfs.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
kgdb.c kgdb: add missing __percpu markup in arch/x86/kernel/kgdb.c 2010-08-16 15:58:30 -05:00
kprobes.c kprobes/x86: Fix the return address of multiple kretprobes 2010-08-19 12:49:56 +02:00
kvm.c
kvmclock.c x86, paravirt: don't compute pvclock adjustments if we trust the tsc 2010-05-19 11:41:05 +03:00
ldt.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
machine_kexec_32.c Merge branch 'x86-mm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2009-12-08 13:27:33 -08:00
machine_kexec_64.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
Makefile x86, olpc: Add support for calling into OpenFirmware 2010-06-18 14:54:36 -07:00
mca_32.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
microcode_amd.c Revert "x86: ucode-amd: Load ucode-patches once ..." 2010-01-23 06:21:59 +01:00
microcode_core.c driver core: add devname module aliases to allow module on-demand auto-loading 2010-05-25 15:08:26 -07:00
microcode_intel.c x86: Improve Intel microcode loader performance 2010-03-11 13:49:06 +01:00
mmconf-fam10h_64.c x86: Move range related operation to one file 2010-02-10 17:47:17 -08:00
module.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
mpparse.c x86, apic: Map the local apic when parsing the MP table. 2010-08-05 16:26:42 -07:00
mrst.c Merge branch 'x86-mrst-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2010-08-06 10:06:28 -07:00
msr.c x86: convert cpu notifier to return encapsulate errno value 2010-05-27 09:12:48 -07:00
olpc.c x86, olpc: Constify an olpc_ofw() arg 2010-07-30 18:02:21 -07:00
olpc_ofw.c x86, olpc: Constify an olpc_ofw() arg 2010-07-30 18:02:21 -07:00
paravirt-spinlocks.c locking: Convert __raw_spin* functions to arch_spin* 2009-12-14 23:55:32 +01:00
paravirt.c x86, paravirt: Remove kmap_atomic_pte paravirt op. 2010-02-27 14:41:35 -08:00
paravirt_patch_32.c
paravirt_patch_64.c
pci-calgary_64.c x86, Calgary: Limit the max PHB number to 256 2010-06-30 22:41:42 -07:00
pci-dma.c x86: Detect whether we should use Xen SWIOTLB. 2010-08-02 15:18:33 -04:00
pci-gart_64.c Merge branch 'iommu/fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/joro/linux-2.6-iommu into x86/urgent 2010-04-13 13:24:54 +02:00
pci-nommu.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
pci-swiotlb.c x86: remove unnecessary sync_single_range_* in swiotlb_dma_ops 2010-05-27 09:12:52 -07:00
pcspeaker.c
pmtimer_64.c
probe_roms_32.c
process.c Make do_execve() take a const filename pointer 2010-08-17 18:07:43 -07:00
process_32.c x86, perf: Add power_end event to process_*.c cpu_idle routine 2010-06-18 11:35:10 +02:00
process_64.c x86, perf: Add power_end event to process_*.c cpu_idle routine 2010-06-18 11:35:10 +02:00
ptrace.c hw-breakpoints: Tag ptrace breakpoint as exclude_kernel 2010-05-01 04:32:07 +02:00
pvclock.c x86, paravirt: don't compute pvclock adjustments if we trust the tsc 2010-05-19 11:41:05 +03:00
quirks.c x86: Force HPET readback_cmp for all ATI chipsets 2010-07-15 17:10:02 +02:00
reboot.c x86: Fix rebooting on Dell Precision WorkStation T7400 2010-06-20 09:24:13 +02:00
reboot_fixups_32.c cs5535: move the DIVIL MSR definition into linux/cs5535.h 2009-12-15 08:53:28 -08:00
relocate_kernel_32.S
relocate_kernel_64.S
rtc.c
scx200_32.c
setup.c x86-32: Separate 1:1 pagetables from swapper_pg_dir 2010-08-18 09:17:20 -07:00
setup_percpu.c Fix up trivial spelling errors ('taht' -> 'that') 2010-07-21 09:25:42 -07:00
sfi.c x86, irq: Rename gsi_end gsi_top, and fix off by one errors 2010-06-09 13:34:06 -07:00
signal.c x86: Merge sys_sigaltstack 2009-12-09 16:28:59 -08:00
smp.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
smpboot.c x86, hotplug: Serialize CPU hotplug to avoid bringup concurrency issues 2010-08-19 14:47:43 -07:00
stacktrace.c x86: Unify save_stack_address() and save_stack_address_nosched() 2010-06-09 17:32:19 +02:00
step.c x86, ptrace: Fix block-step 2010-03-26 11:33:57 +01:00
sys_i386_32.c Make do_execve() take a const filename pointer 2010-08-17 18:07:43 -07:00
sys_x86_64.c improve sys_newuname() for compat architectures 2010-03-12 15:52:32 -08:00
syscall_64.c
syscall_table_32.S x86: fix up system call numbering nit 2010-08-10 15:35:10 -07:00
tboot.c Merge branch 'kvm-updates/2.6.35' of git://git.kernel.org/pub/scm/virt/kvm/kvm 2010-05-21 17:16:21 -07:00
tce_64.c
test_nx.c
test_rodata.c
time.c x86: Convert i8259_lock to raw_spinlock 2010-02-16 18:21:32 +01:00
tlb_uv.c x86, UV: Initialize BAU hub map 2010-08-01 09:18:41 +02:00
tls.c
tls.h
topology.c
trampoline.c x86, mm: Fix CONFIG_VMSPLIT_1G and 2G_OPT trampoline 2010-08-24 23:05:17 -07:00
trampoline_32.S
trampoline_64.S
traps.c Merge branch 'perf/nmi' into perf/core 2010-08-05 08:45:05 +02:00
tsc.c x86, tsc: Fix a preemption leak in restore_sched_clock_state() 2010-09-10 18:17:45 -07:00
tsc_sync.c locking: Convert __raw_spin* functions to arch_spin* 2009-12-14 23:55:32 +01:00
uv_irq.c Merge branch 'x86-uv-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2010-05-18 09:46:35 -07:00
uv_sysfs.c x86: Remove trailing spaces in messages 2010-02-07 17:47:51 +01:00
uv_time.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
verify_cpu_64.S x86: Use symbolic MSR names 2010-07-21 21:23:40 -07:00
visws_quirks.c Merge remote branch 'origin/x86/apic' into x86/mrst 2010-02-22 16:25:18 -08:00
vm86_32.c x86, 32-bit: Convert sys_vm86 & sys_vm86old 2009-12-09 16:29:23 -08:00
vmi_32.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
vmiclock_32.c Merge branch 'for-next' into for-linus 2010-03-08 16:55:37 +01:00
vmlinux.lds.S Merge branch 'for-35' of git://repo.or.cz/linux-kbuild 2010-06-01 08:55:52 -07:00
vsmp_64.c
vsyscall_64.c timkeeping: Fix update_vsyscall to provide wall_to_monotonic offset 2010-07-27 12:40:54 +02:00
x86_init.c x86: Add i8042 pre-detection hook to x86_platform_ops 2010-07-07 17:05:06 -07:00
x8664_ksyms_64.c x86-64: Don't export init_level4_pgt 2010-04-28 17:25:47 -07:00
xsave.c Merge branch 'x86-xsave-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2010-08-06 16:25:13 -07:00