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

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Date:	Sun, 29 Jun 2014 13:01:08 +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,
	Oren Twaig <oren@...lemp.com>
Subject: [PATCH v2] x86, vsmp: Remove is_vsmp_box() from apic_is_clustered_box()

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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