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Date: Tue, 30 Oct 2012 18:05:02 -0700
From: Venki Pallipadi <venki@...gle.com>
To: Suresh Siddha <suresh.b.siddha@...el.com>
Cc: Thomas Gleixner <tglx@...utronix.de>,
"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
"Brown, Len" <len.brown@...el.com>
Subject: Re: [patch] x86, apic: use tsc deadline for oneshot when available
Patch looks good.
Acked-by: Venkatesh Pallipadi <venki@...gle.com>
On Mon, Oct 22, 2012 at 2:37 PM, Suresh Siddha
<suresh.b.siddha@...el.com> wrote:
>
> Thomas, You wanted to run some tests with this, right? Please give it a
> try and see if this is ok to be pushed to the -tip.
>
> thanks,
> suresh
> --8<--
> From: Suresh Siddha <suresh.b.siddha@...el.com>
> Subject: x86, apic: use tsc deadline for oneshot when available
>
> If the TSC deadline mode is supported, LAPIC timer one-shot mode can be
> implemented using IA32_TSC_DEADLINE MSR. An interrupt will be generated
> when the TSC value equals or exceeds the value in the IA32_TSC_DEADLINE
> MSR.
>
> This enables us to skip the APIC calibration during boot. Also,
> in xapic mode, this enables us to skip the uncached apic access
> to re-arm the APIC timer.
>
> As this timer ticks at the high frequency TSC rate, we use the
> TSC_DIVISOR (32) to work with the 32-bit restrictions in the clockevent
> API's to avoid 64-bit divides etc (frequency is u32 and "unsigned long"
> in the set_next_event(), max_delta limits the next event to 32-bit for
> 32-bit kernel).
>
> Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
> ---
> Documentation/kernel-parameters.txt | 4 ++
> arch/x86/include/asm/msr-index.h | 2 +
> arch/x86/kernel/apic/apic.c | 66 ++++++++++++++++++++++++++---------
> 3 files changed, 55 insertions(+), 17 deletions(-)
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 9776f06..4aa9ca0 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -1304,6 +1304,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
> lapic [X86-32,APIC] Enable the local APIC even if BIOS
> disabled it.
>
> + lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
> + value for LAPIC timer one-shot implementation. Default
> + back to the programmable timer unit in the LAPIC.
> +
> lapic_timer_c2_ok [X86,APIC] trust the local apic timer
> in C2 power state.
>
> diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
> index 7f0edce..e400cdb 100644
> --- a/arch/x86/include/asm/msr-index.h
> +++ b/arch/x86/include/asm/msr-index.h
> @@ -337,6 +337,8 @@
> #define MSR_IA32_MISC_ENABLE_TURBO_DISABLE (1ULL << 38)
> #define MSR_IA32_MISC_ENABLE_IP_PREF_DISABLE (1ULL << 39)
>
> +#define MSR_IA32_TSC_DEADLINE 0x000006E0
> +
> /* P4/Xeon+ specific */
> #define MSR_IA32_MCG_EAX 0x00000180
> #define MSR_IA32_MCG_EBX 0x00000181
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index b17416e..b0c49b1 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -90,21 +90,6 @@ EXPORT_EARLY_PER_CPU_SYMBOL(x86_bios_cpu_apicid);
> */
> DEFINE_EARLY_PER_CPU_READ_MOSTLY(int, x86_cpu_to_logical_apicid, BAD_APICID);
>
> -/*
> - * Knob to control our willingness to enable the local APIC.
> - *
> - * +1=force-enable
> - */
> -static int force_enable_local_apic __initdata;
> -/*
> - * APIC command line parameters
> - */
> -static int __init parse_lapic(char *arg)
> -{
> - force_enable_local_apic = 1;
> - return 0;
> -}
> -early_param("lapic", parse_lapic);
> /* Local APIC was disabled by the BIOS and enabled by the kernel */
> static int enabled_via_apicbase;
>
> @@ -133,6 +118,25 @@ static inline void imcr_apic_to_pic(void)
> }
> #endif
>
> +/*
> + * Knob to control our willingness to enable the local APIC.
> + *
> + * +1=force-enable
> + */
> +static int force_enable_local_apic __initdata;
> +/*
> + * APIC command line parameters
> + */
> +static int __init parse_lapic(char *arg)
> +{
> + if (config_enabled(CONFIG_X86_32) && !arg)
> + force_enable_local_apic = 1;
> + else if (!strncmp(arg, "notscdeadline", 13))
> + setup_clear_cpu_cap(X86_FEATURE_TSC_DEADLINE_TIMER);
> + return 0;
> +}
> +early_param("lapic", parse_lapic);
> +
> #ifdef CONFIG_X86_64
> static int apic_calibrate_pmtmr __initdata;
> static __init int setup_apicpmtimer(char *s)
> @@ -315,6 +319,7 @@ int lapic_get_maxlvt(void)
>
> /* Clock divisor */
> #define APIC_DIVISOR 16
> +#define TSC_DIVISOR 32
>
> /*
> * This function sets up the local APIC timer, with a timeout of
> @@ -333,6 +338,9 @@ static void __setup_APIC_LVTT(unsigned int clocks, int oneshot, int irqen)
> lvtt_value = LOCAL_TIMER_VECTOR;
> if (!oneshot)
> lvtt_value |= APIC_LVT_TIMER_PERIODIC;
> + else if (boot_cpu_has(X86_FEATURE_TSC_DEADLINE_TIMER))
> + lvtt_value |= APIC_LVT_TIMER_TSCDEADLINE;
> +
> if (!lapic_is_integrated())
> lvtt_value |= SET_APIC_TIMER_BASE(APIC_TIMER_BASE_DIV);
>
> @@ -341,6 +349,11 @@ static void __setup_APIC_LVTT(unsigned int clocks, int oneshot, int irqen)
>
> apic_write(APIC_LVTT, lvtt_value);
>
> + if (lvtt_value & APIC_LVT_TIMER_TSCDEADLINE) {
> + printk_once(KERN_DEBUG "TSC deadline timer enabled\n");
> + return;
> + }
> +
> /*
> * Divide PICLK by 16
> */
> @@ -453,6 +466,15 @@ static int lapic_next_event(unsigned long delta,
> return 0;
> }
>
> +static int lapic_next_deadline(unsigned long delta,
> + struct clock_event_device *evt)
> +{
> + u64 tsc;
> + rdtscll(tsc);
> + wrmsrl(MSR_IA32_TSC_DEADLINE, tsc + (((u64) delta) * TSC_DIVISOR));
> + return 0;
> +}
> +
> /*
> * Setup the lapic timer in periodic or oneshot mode
> */
> @@ -533,7 +555,15 @@ static void __cpuinit setup_APIC_timer(void)
> memcpy(levt, &lapic_clockevent, sizeof(*levt));
> levt->cpumask = cpumask_of(smp_processor_id());
>
> - clockevents_register_device(levt);
> + if (this_cpu_has(X86_FEATURE_TSC_DEADLINE_TIMER)) {
> + levt->features &= ~(CLOCK_EVT_FEAT_PERIODIC |
> + CLOCK_EVT_FEAT_DUMMY);
> + levt->set_next_event = lapic_next_deadline;
> + clockevents_config_and_register(levt,
> + (tsc_khz / TSC_DIVISOR) * 1000,
> + 0xF, ~0UL);
> + } else
> + clockevents_register_device(levt);
> }
>
> /*
> @@ -661,7 +691,9 @@ static int __init calibrate_APIC_clock(void)
> * in the clockevent structure and return.
> */
>
> - if (lapic_timer_frequency) {
> + if (boot_cpu_has(X86_FEATURE_TSC_DEADLINE_TIMER)) {
> + return 0;
> + } else if (lapic_timer_frequency) {
> apic_printk(APIC_VERBOSE, "lapic timer already calibrated %d\n",
> lapic_timer_frequency);
> lapic_clockevent.mult = div_sc(lapic_timer_frequency/APIC_DIVISOR,
>
>
--
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