linux-kernel - Re: [PATCH v4] vsmp: Fix number of CPUs when vsmp is disabled

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Date:	Fri, 11 May 2012 22:26:31 +0300
From:	Ido Yariv <ido@...ery.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Shai Fultheim <shai@...lemp.com>
Subject: Re: [PATCH v4] vsmp: Fix number of CPUs when vsmp is disabled

Hi,

On Wed, May 09, 2012 at 08:55:54AM -0700, H. Peter Anvin wrote:
> On 05/09/2012 08:44 AM, Ingo Molnar wrote:
> > 
> > * Ido Yariv <ido@...ery.com> wrote:
> > 
> >> +static void __init vsmp_cap_cpus(void)
> >> +{
> >> +	void __iomem *address;
> >> +	unsigned int cfg, topology, node_shift, maxcpus;
> >> +
> >> +#ifdef CONFIG_X86_VSMP
> >> +	/* VSMP is enabled, no need to cap cpus */
> >> +	return;
> >> +#elif defined(CONFIG_SMP)
> >> +	/*
> >> +	 * CONFIG_X86_VSMP is not configured, so limit the number CPUs to the
> > 
> > I suspect this will throw compiler warnings in the 
> > CONFIG_X86_VSMP && !CONFIG_SMP case.
> > 
> 
> What on Earth is the point of allowing that combination?  Why not make
> X86_VSMP depend on SMP and reduce the testing matrix?

CONFIG_X86_VSMP shouldn't be used without CONFIG_SMP, so we can safely
add this dependency.
Ingo's suggestion will still fix unreferenced variables warnings, so how
about the following patch?

Thanks,
Ido.

>From 6fa023be44749092088618379f13d7a3e086d692 Mon Sep 17 00:00:00 2001
From: Shai Fultheim <shai@...lemp.com>
Date: Mon, 16 Apr 2012 10:39:35 +0300
Subject: [PATCH v5] vsmp: Fix number of CPUs when vsmp is disabled

In case CONFIG_X86_VSMP is not set, limit the number of CPUs to the
number of CPUs of the first board.

Also make CONFIG_X86_VSMP depend on CONFIG_SMP, as there's little
point in having a vsmp machine with a single CPU.

Signed-off-by: Shai Fultheim <shai@...lemp.com>
[ido@...ery.com: rebased, fixed minor coding-style issues]
Signed-off-by: Ido Yariv <ido@...ery.com>
---
 arch/x86/Kconfig          |    1 +
 arch/x86/kernel/vsmp_64.c |   40 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 0 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index c9866b0..b1e98c9 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -374,6 +374,7 @@ config X86_VSMP
 	select PARAVIRT
 	depends on X86_64 && PCI
 	depends on X86_EXTENDED_PLATFORM
+	depends on SMP
 	---help---
 	  Support for ScaleMP vSMP systems.  Say 'Y' here if this kernel is
 	  supposed to run on these EM64T-based machines.  Only choose this option
diff --git a/arch/x86/kernel/vsmp_64.c b/arch/x86/kernel/vsmp_64.c
index a1d804b..8eeb55a 100644
--- a/arch/x86/kernel/vsmp_64.c
+++ b/arch/x86/kernel/vsmp_64.c
@@ -15,6 +15,7 @@
 #include <linux/init.h>
 #include <linux/pci_ids.h>
 #include <linux/pci_regs.h>
+#include <linux/smp.h>
 
 #include <asm/apic.h>
 #include <asm/pci-direct.h>
@@ -22,6 +23,8 @@
 #include <asm/paravirt.h>
 #include <asm/setup.h>
 
+#define TOPOLOGY_REGISTER_OFFSET 0x10
+
 #if defined CONFIG_PCI && defined CONFIG_PARAVIRT
 /*
  * Interrupt control on vSMPowered systems:
@@ -149,12 +152,49 @@ int is_vsmp_box(void)
 	return 0;
 }
 #endif
+
+static void __init vsmp_cap_cpus(void)
+{
+#if !defined(CONFIG_X86_VSMP) && defined(CONFIG_SMP)
+	void __iomem *address;
+	unsigned int cfg, topology, node_shift, maxcpus;
+
+	/*
+	 * CONFIG_X86_VSMP is not configured, so limit the number CPUs to the
+	 * ones present in the first board, unless explicitly overridden by
+	 * setup_max_cpus
+	 */
+	if (setup_max_cpus != NR_CPUS)
+		return;
+
+	/* Read the vSMP Foundation topology register */
+	cfg = read_pci_config(0, 0x1f, 0, PCI_BASE_ADDRESS_0);
+	address = early_ioremap(cfg + TOPOLOGY_REGISTER_OFFSET, 4);
+	if (WARN_ON(!address))
+		return;
+
+	topology = readl(address);
+	node_shift = (topology >> 16) & 0x7;
+	if (!node_shift)
+		/* The value 0 should be decoded as 8 */
+		node_shift = 8;
+	maxcpus = (topology & ((1 << node_shift) - 1)) + 1;
+
+	pr_info("vSMP CTL: Capping CPUs to %d (CONFIG_X86_VSMP is unset)\n",
+		maxcpus);
+	setup_max_cpus = maxcpus;
+	early_iounmap(address, 4);
+#endif
+}
+
 void __init vsmp_init(void)
 {
 	detect_vsmp_box();
 	if (!is_vsmp_box())
 		return;
 
+	vsmp_cap_cpus();
+
 	set_vsmp_pv_ops();
 	return;
 }
-- 
1.7.6.5

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