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

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Date:	Mon, 23 Jun 2014 08:35:14 +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,
	Shai Fultheim <shai@...lemp.com>, Oren Twaig <oren@...lemp.com>
Subject: [PATCH] x86, vsmp: Remove is_vsmp_box() from apic_is_clustered_box()

Remove invalid code which caused TSC to be declared as "unstable" on vSMP
Foundation box even if it was stable and let the kernel decide for itself.

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.

Signed-off-by: Oren Twaig <oren@...lemp.com>
Acked-by: Shai Fultheim <shai@...lemp.com>
---
 arch/x86/include/asm/apic.h |    8 ------
 arch/x86/kernel/apic/apic.c |   60 +------------------------------------------
 2 files changed, 1 insertion(+), 67 deletions(-)

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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