linux-kernel - Re: [patch 4/4] x86: apic_is_clustered_box to indicate unsynched TSC's on multiboard vSMP systems

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Date:	Mon, 24 Mar 2008 14:48:36 -0700
From:	Ravikiran G Thirumalai <kiran@...lex86.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Yinghai Lu <yhlu.kernel@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Glauber de Oliveira Costa <gcosta@...hat.com>,
	shai@...lex86.org
Subject: Re: [patch 4/4] x86: apic_is_clustered_box to indicate unsynched TSC's on multiboard vSMP systems

On Sat, Mar 22, 2008 at 09:02:51PM +0100, Ingo Molnar wrote:
>
>* Ravikiran G Thirumalai <kiran@...lex86.org> wrote:
>
>> OK. Something like this?
>
>yeah.
>
>small nit:
>
>> +int is_vsmp_box(void)
>> +{
>> +	if (is_vsmp != -1)
>> +		return is_vsmp;
>> +	else {
>> +		printk("ScaleMP vSMPowered system detection called too early!\n");
>> +		return 0;
>> +	}
>>  }
>
>since this is an "impossible" scenario, just stick in a WARN_ON_ONCE().
>

Sure.  Here's the modified patch.

vSMP detection: Access pci config space early in boot to detect if the
system is a vSMPowered box, and cache the result in a flag, so that
is_vsmp_box() retrieves the value of the flag always.

Signed-off-by; Ravikiran Thirumalai <kiran@...lex86.org>

Index: linux.git.trees/arch/x86/kernel/vsmp_64.c
===================================================================
--- linux.git.trees.orig/arch/x86/kernel/vsmp_64.c	2008-03-21 13:15:17.000000000 -0700
+++ linux.git.trees/arch/x86/kernel/vsmp_64.c	2008-03-24 13:57:09.387437626 -0700
@@ -108,25 +108,34 @@ static void __init set_vsmp_pv_ops(void)
 #endif
 
 #ifdef CONFIG_PCI
-static int vsmp = -1;
+static int is_vsmp = -1;
 
-int is_vsmp_box(void)
+static void __init detect_vsmp_box(void)
 {
-	if (vsmp != -1)
-		return vsmp;
+	is_vsmp = 0;
 
-	vsmp = 0;
 	if (!early_pci_allowed())
-		return vsmp;
+		return;
 
-	/* Check if we are running on a ScaleMP vSMP box */
+	/* Check if we are running on a ScaleMP vSMPowered box */
 	if (read_pci_config(0, 0x1f, 0, PCI_VENDOR_ID) ==
 	     (PCI_VENDOR_ID_SCALEMP | (PCI_DEVICE_ID_SCALEMP_VSMP_CTL << 16)))
-		vsmp = 1;
+		is_vsmp = 1;
+}
 
-	return vsmp;
+int is_vsmp_box(void)
+{
+	if (is_vsmp != -1)
+		return is_vsmp;
+	else {
+		WARN_ON_ONCE(1);
+		return 0;
+	}
 }
 #else
+static int __init detect_vsmp_box(void)
+{
+}
 int is_vsmp_box(void)
 {
 	return 0;
@@ -135,6 +144,7 @@ int is_vsmp_box(void)
 
 void __init vsmp_init(void)
 {
+	detect_vsmp_box();
 	if (!is_vsmp_box())
 		return;
 
--
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