Re: [PATCH -v2] x86, tsc: Limit CPU frequency calibration on AMD

[Alok Kataria]

Hi Borislav,

Thanks for working on this change..

On Tue, 2010-08-24 at 08:53 -0700, Borislav Petkov wrote:
> 6b37f5a20c0e5c334c010a587058354215433e92 introduced the CPU frequency
> calibration code for AMD CPUs whose TSCs didn't increment with the
> core's P0 frequency. From F10h, revB onward, the TSC increment rate is
> denoted by MSRC001_0015[24] and when this bit is set (which is normally
> done by the BIOS,) the TSC increments with the P0 frequency so the
> calibration is not needed and booting can be a couple of mcecs faster on
> those machines.
> 
> While at it, make the code work on 32-bit. In addition, use the 4th
> perfctr since using perfctr 0 might clash with perfctr-watchdog.c during
> LAPIC init. Finally, warn about wrongly calibrated value in the most
> seldom cases when the core TSC is not incrementing with P0 frequency.
> 
> Signed-off-by: Borislav Petkov <borislav.petkov@xxxxxxx>
> ---
> 
> Here's the new version, had to change quite a lot and check all families
> first.
> 
> @Alok, I think in your case you will want to do
> 
> 	x86_cpuinit.calibrate_cpu = NULL;

> since this means no need to recalibrate.

Right, I will send that patch once this is committed. 

Alok
> 
> Sorry for the delay.
> 
> 
>  arch/x86/include/asm/x86_init.h |    1 +
>  arch/x86/kernel/cpu/amd.c       |   74 +++++++++++++++++++++++++++++++++++++++
>  arch/x86/kernel/tsc.c           |   65 ++++------------------------------
>  3 files changed, 83 insertions(+), 57 deletions(-)
> 
> diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h
> index baa579c..c63ab76 100644
> --- a/arch/x86/include/asm/x86_init.h
> +++ b/arch/x86/include/asm/x86_init.h
> @@ -133,6 +133,7 @@ struct x86_init_ops {
>   */
>  struct x86_cpuinit_ops {
>  	void (*setup_percpu_clockev)(void);
> +	unsigned long (*calibrate_cpu)(void);
>  };
>  
>  /**
> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> index ba5f62f..236bcff 100644
> --- a/arch/x86/kernel/cpu/amd.c
> +++ b/arch/x86/kernel/cpu/amd.c
> @@ -6,6 +6,7 @@
>  #include <asm/processor.h>
>  #include <asm/apic.h>
>  #include <asm/cpu.h>
> +#include <asm/nmi.h>
>  #include <asm/pci-direct.h>
>  
>  #ifdef CONFIG_X86_64
> @@ -381,6 +382,62 @@ static void __cpuinit early_init_amd_mc(struct cpuinfo_x86 *c)
>  #endif
>  }
>  
> +/*
> + * This is used on systems with fixed rate TSCs to determine processor frequency
> + * when the TSC on those systems is not incrementing with the P0 frequency.
> + */
> +#define TICK_COUNT 100000000
> +unsigned long __cpuinit amd_calibrate_cpu(void)
> +{
> +	u64 evntsel3 = 0, pmc3 = 0, pmcs = 0;
> +	int tsc_start, tscs, i, no_ctr_free;
> +	unsigned long flags;
> +
> +	for (i = 3; i >= -1; i--)
> +		if (avail_to_resrv_perfctr_nmi_bit(i))
> +			break;
> +
> +	no_ctr_free = (i == -1);
> +	if (no_ctr_free) {
> +		WARN(1, KERN_WARNING "Warning: AMD perfctrs busy ... "
> +		     "cpu_khz value may be incorrect.\n");
> +		i = 3;
> +		rdmsrl(MSR_K7_EVNTSEL3, evntsel3);
> +		wrmsrl(MSR_K7_EVNTSEL3, 0);
> +		rdmsrl(MSR_K7_PERFCTR3, pmc3);
> +	} else {
> +		reserve_perfctr_nmi(MSR_K7_PERFCTR0 + i);
> +		reserve_evntsel_nmi(MSR_K7_EVNTSEL0 + i);
> +	}
> +
> +	/* start measuring cycles, incrementing from 0 */
> +	local_irq_save(flags);
> +	wrmsrl(MSR_K7_PERFCTR0 + i, 0);
> +	wrmsrl(MSR_K7_EVNTSEL0 + i, 1 << 22 | 3 << 16 | 0x76);
> +	rdtscl(tsc_start);
> +	do {
> +		rdmsrl(MSR_K7_PERFCTR0 + i, pmcs);
> +		tscs = get_cycles();
> +	} while ((tscs - tsc_start) < TICK_COUNT);
> +	local_irq_restore(flags);
> +
> +	if (no_ctr_free) {
> +		wrmsrl(MSR_K7_EVNTSEL3, 0);
> +		wrmsrl(MSR_K7_PERFCTR3, pmc3);
> +		wrmsrl(MSR_K7_EVNTSEL3, evntsel3);
> +	} else {
> +		release_perfctr_nmi(MSR_K7_PERFCTR0 + i);
> +		release_evntsel_nmi(MSR_K7_EVNTSEL0 + i);
> +	}
> +
> +	pmcs *= tsc_khz;
> +	tscs -= tsc_start;
> +
> +	(void)do_div(pmcs, tscs);
> +
> +	return pmcs;
> +}
> +
>  static void __cpuinit early_init_amd(struct cpuinfo_x86 *c)
>  {
>  	early_init_amd_mc(c);
> @@ -412,6 +469,23 @@ static void __cpuinit early_init_amd(struct cpuinfo_x86 *c)
>  			set_cpu_cap(c, X86_FEATURE_EXTD_APICID);
>  	}
>  #endif
> +
> +	/* We need to do the following only once */
> +	if (c != &boot_cpu_data)
> +		return;
> +
> +	if (cpu_has(c, X86_FEATURE_CONSTANT_TSC)) {
> +
> +		if (c->x86 > 0x10 ||
> +		    (c->x86 == 0x10 && c->x86_model >= 0x2)) {
> +			u64 val;
> +
> +			rdmsrl(MSR_K7_HWCR, val);
> +			if (!(val & BIT(24)))
> +				x86_cpuinit.calibrate_cpu = amd_calibrate_cpu;
> +		} else
> +			x86_cpuinit.calibrate_cpu = amd_calibrate_cpu;
> +	}
>  }
>  
>  static void __cpuinit init_amd(struct cpuinfo_x86 *c)
> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> index ce8e502..6b4f22f 100644
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -854,60 +854,6 @@ static void __init init_tsc_clocksource(void)
>  	clocksource_register_khz(&clocksource_tsc, tsc_khz);
>  }
>  
> -#ifdef CONFIG_X86_64
> -/*
> - * calibrate_cpu is used on systems with fixed rate TSCs to determine
> - * processor frequency
> - */
> -#define TICK_COUNT 100000000
> -static unsigned long __init calibrate_cpu(void)
> -{
> -	int tsc_start, tsc_now;
> -	int i, no_ctr_free;
> -	unsigned long evntsel3 = 0, pmc3 = 0, pmc_now = 0;
> -	unsigned long flags;
> -
> -	for (i = 0; i < 4; i++)
> -		if (avail_to_resrv_perfctr_nmi_bit(i))
> -			break;
> -	no_ctr_free = (i == 4);
> -	if (no_ctr_free) {
> -		WARN(1, KERN_WARNING "Warning: AMD perfctrs busy ... "
> -		     "cpu_khz value may be incorrect.\n");
> -		i = 3;
> -		rdmsrl(MSR_K7_EVNTSEL3, evntsel3);
> -		wrmsrl(MSR_K7_EVNTSEL3, 0);
> -		rdmsrl(MSR_K7_PERFCTR3, pmc3);
> -	} else {
> -		reserve_perfctr_nmi(MSR_K7_PERFCTR0 + i);
> -		reserve_evntsel_nmi(MSR_K7_EVNTSEL0 + i);
> -	}
> -	local_irq_save(flags);
> -	/* start measuring cycles, incrementing from 0 */
> -	wrmsrl(MSR_K7_PERFCTR0 + i, 0);
> -	wrmsrl(MSR_K7_EVNTSEL0 + i, 1 << 22 | 3 << 16 | 0x76);
> -	rdtscl(tsc_start);
> -	do {
> -		rdmsrl(MSR_K7_PERFCTR0 + i, pmc_now);
> -		tsc_now = get_cycles();
> -	} while ((tsc_now - tsc_start) < TICK_COUNT);
> -
> -	local_irq_restore(flags);
> -	if (no_ctr_free) {
> -		wrmsrl(MSR_K7_EVNTSEL3, 0);
> -		wrmsrl(MSR_K7_PERFCTR3, pmc3);
> -		wrmsrl(MSR_K7_EVNTSEL3, evntsel3);
> -	} else {
> -		release_perfctr_nmi(MSR_K7_PERFCTR0 + i);
> -		release_evntsel_nmi(MSR_K7_EVNTSEL0 + i);
> -	}
> -
> -	return pmc_now * tsc_khz / (tsc_now - tsc_start);
> -}
> -#else
> -static inline unsigned long calibrate_cpu(void) { return cpu_khz; }
> -#endif
> -
>  void __init tsc_init(void)
>  {
>  	u64 lpj;
> @@ -926,9 +872,14 @@ void __init tsc_init(void)
>  		return;
>  	}
>  
> -	if (cpu_has(&boot_cpu_data, X86_FEATURE_CONSTANT_TSC) &&
> -			(boot_cpu_data.x86_vendor == X86_VENDOR_AMD))
> -		cpu_khz = calibrate_cpu();
> +	if (x86_cpuinit.calibrate_cpu) {
> +		cpu_khz = x86_cpuinit.calibrate_cpu();
> +		if (cpu_khz < tsc_khz) {
> +			printk(KERN_WARNING "TSC possibly calibrated at non-P0 "
> +			      "core frequency, fall back to previous value.\n");
> +			cpu_khz = tsc_khz;
> +		}
> +	}
>  
>  	printk("Detected %lu.%03lu MHz processor.\n",
>  			(unsigned long)cpu_khz / 1000,
> -- 
> 1.7.1
> 

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