linux-kernel - Re: [PATCH v2] x86, vsmp: Remove is_vsmp_box() from apic_is_clustered

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Date:	Sun, 06 Jul 2014 09:32:51 +0300
From:	Oren Twaig <oren@...lemp.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	David Rientjes <rientjes@...gle.com>,
	Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	Andi Kleen <ak@...ux.intel.com>,
	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>,
	Richard Weinberger <richard@....at>
CC:	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] x86, vsmp: Remove is_vsmp_box() from apic_is_clustered_box()

Hi,

Quick question: As I'm new at this (submitting patches), what is a reasonable time to wait before ping-ing a patch ?

Oren.

On 06/29/2014 01:01 PM, Oren Twaig wrote:
> When a vSMP Foundation box is detected, the function apic_cluster_num() counts
> the number of APIC clusters found. If more than one found, a multi board
> configuration is assumed, and TSC marked as unstable. This behavior is
> incorrect as vSMP Foundation may use processors from single node only, attached
> to memory of other nodes - and such node may have more than one APIC cluster
> (typically any recent intel box has more than single APIC_CLUSTERID(x)).
>
> To fix this, we simply remove the code which detects a vSMP Foundation box and
> affects apic_is_clusted_box() return value. This can be done because later the
> kernel checks by itself if the TSC is stable using the
> check_tsc_sync_[source|target]() functions and marks TSC as unstable if needed.
>
> Acked-by: Shai Fultheim <shai@...lemp.com>
> Signed-off-by: Oren Twaig <oren@...lemp.com>
> ---
> diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
> index 19b0eba..c100694 100644
> --- a/arch/x86/include/asm/apic.h
> +++ b/arch/x86/include/asm/apic.h
> @@ -85,14 +85,6 @@ static inline bool apic_from_smp_config(void)
>  #include <asm/paravirt.h>
>  #endif
>  
> -#ifdef CONFIG_X86_64
> -extern int is_vsmp_box(void);
> -#else
> -static inline int is_vsmp_box(void)
> -{
> -	return 0;
> -}
> -#endif
>  extern int setup_profiling_timer(unsigned int);
>  
>  static inline void native_apic_mem_write(u32 reg, u32 v)
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index ad28db7..2b85bb9 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -2451,51 +2451,6 @@ static void apic_pm_activate(void) { }
>  
>  #ifdef CONFIG_X86_64
>  
> -static int apic_cluster_num(void)
> -{
> -	int i, clusters, zeros;
> -	unsigned id;
> -	u16 *bios_cpu_apicid;
> -	DECLARE_BITMAP(clustermap, NUM_APIC_CLUSTERS);
> -
> -	bios_cpu_apicid = early_per_cpu_ptr(x86_bios_cpu_apicid);
> -	bitmap_zero(clustermap, NUM_APIC_CLUSTERS);
> -
> -	for (i = 0; i < nr_cpu_ids; i++) {
> -		/* are we being called early in kernel startup? */
> -		if (bios_cpu_apicid) {
> -			id = bios_cpu_apicid[i];
> -		} else if (i < nr_cpu_ids) {
> -			if (cpu_present(i))
> -				id = per_cpu(x86_bios_cpu_apicid, i);
> -			else
> -				continue;
> -		} else
> -			break;
> -
> -		if (id != BAD_APICID)
> -			__set_bit(APIC_CLUSTERID(id), clustermap);
> -	}
> -
> -	/* Problem:  Partially populated chassis may not have CPUs in some of
> -	 * the APIC clusters they have been allocated.  Only present CPUs have
> -	 * x86_bios_cpu_apicid entries, thus causing zeroes in the bitmap.
> -	 * Since clusters are allocated sequentially, count zeros only if
> -	 * they are bounded by ones.
> -	 */
> -	clusters = 0;
> -	zeros = 0;
> -	for (i = 0; i < NUM_APIC_CLUSTERS; i++) {
> -		if (test_bit(i, clustermap)) {
> -			clusters += 1 + zeros;
> -			zeros = 0;
> -		} else
> -			++zeros;
> -	}
> -
> -	return clusters;
> -}
> -
>  static int multi_checked;
>  static int multi;
>  
> @@ -2540,20 +2495,7 @@ static void dmi_check_multi(void)
>  int apic_is_clustered_box(void)
>  {
>  	dmi_check_multi();
> -	if (multi)
> -		return 1;
> -
> -	if (!is_vsmp_box())
> -		return 0;
> -
> -	/*
> -	 * ScaleMP vSMPowered boxes have one cluster per board and TSCs are
> -	 * not guaranteed to be synced between boards
> -	 */
> -	if (apic_cluster_num() > 1)
> -		return 1;
> -
> -	return 0;
> +	return multi;
>  }
>  #endif
>  
>

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