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From: Venkatesh Pallipadi on 28 Jul 2010 16:40
On Tue, Jul 27, 2010 at 9:37 PM, Len Brown <lenb(a)kernel.org> wrote:
> From: Len Brown <len.brown(a)intel.com>
>
> The LOCAL APIC on new processors has a mode where
> its underlying hardware timer can now be accessed
> via the non-serializing IA32_TSC_DEADLINE_MSR in TSC tick units.
>
> If this mode is present, prefer it over the
> traditional LAPIC timer mode. �KERN_DEBUG dmesg
> will print "TSC deadline timer enabled" when TDT is used.
>
> Bootparam "tdt_off" is available to revert to LAPIC timer mode.
>
> This patch is based on original work by Venkatesh Pallipadi.
>
> cc: Venkatesh Pallipadi <venki(a)google.com>
> Signed-off-by: Len Brown <len.brown(a)intel.com>
> ---
> �Documentation/kernel-parameters.txt | � �3 ++
> �arch/x86/kernel/apic/apic.c � � � � | � 44 ++++++++++++++++++++++++++++++++++-
> �2 files changed, 46 insertions(+), 1 deletions(-)
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 2b2407d..73ec308 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -2596,6 +2596,9 @@ and is between 256 and 4096 characters. It is defined in the file
>
> � � � �tdfx= � � � � � [HW,DRM]
>
> + � � � tdt_off � � � � [APIC,X86]
> + � � � � � � � � � � � Disable TSC Deadline Timer, default back to LAPIC timer.
> +

How about renaming this to noapictdt or nolapictdt? Not that they are
good, but that would make it similar to other apic params.

> � � � �test_suspend= � [SUSPEND]
> � � � � � � � � � � � �Specify "mem" (for Suspend-to-RAM) or "standby" (for
> � � � � � � � � � � � �standby suspend) as the system sleep state to briefly
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index a96489e..64069ae 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -53,6 +53,15 @@
> �#include <asm/kvm_para.h>
> �#include <asm/tsc.h>
>
> +#define APIC_TIMER_MODE_ONESHOT � � � � � � � �(0 << 17)
> +#define APIC_TIMER_MODE_PERIODIC � � � (1 << 17)
> +#define APIC_TIMER_MODE_TSC_DEADLINE � (2 << 17)
> +#define APIC_TIMER_MODE_MASK � � � � � (3 << 17)
> +
> +static unsigned long tsc_per_apic_clock;
> +static int tdt_enabled;
> +static int tdt_disable;
> +
> �unsigned int num_processors;
>
> �unsigned disabled_cpus __cpuinitdata;
> @@ -355,6 +364,14 @@ static void __setup_APIC_LVTT(unsigned int clocks, int oneshot, int irqen)
> � � � �if (!irqen)
> � � � � � � � �lvtt_value |= APIC_LVT_MASKED;
>
> + � � � if (oneshot && !tdt_disable &&
> + � � � � � boot_cpu_has(X86_FEATURE_TSC_DEADLINE)) {
> + � � � � � � � printk_once(KERN_DEBUG "TSC deadline timer enabled\n");
> + � � � � � � � tdt_enabled = 1;
> + � � � � � � � lvtt_value &= (~APIC_TIMER_MODE_MASK);
> + � � � � � � � lvtt_value |= APIC_TIMER_MODE_TSC_DEADLINE;
> + � � � }
> +
> � � � �apic_write(APIC_LVTT, lvtt_value);
>
> � � � �/*
> @@ -409,7 +426,20 @@ EXPORT_SYMBOL_GPL(setup_APIC_eilvt_ibs);
> �static int lapic_next_event(unsigned long delta,
> � � � � � � � � � � � � � �struct clock_event_device *evt)
> �{
> - � � � apic_write(APIC_TMICT, delta);
> + � � � if (tdt_enabled) {
> + � � � � � � � u64 tsc;
> + � � � � � � � u64 delta_tsc;
> +
> + � � � � � � � delta_tsc = delta * tsc_per_apic_clock;

About this conversion. I think it is cleaner and probably better in
terms of performance to deal with TSC natively in lapic_clockevent.
That would mean having the mult and min/max delta in terms of TSC.
That would also mean we can avoid APIC tick frequency calibration.
Also, having a different ->next_event for TSC deadline timer would be
better than checking this flag on every call.

Thanks,
Venki
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Next: jump label v10: convert jump label to use a key