linux-kernel - Re: [tip:x86/platform] x86/vsmp: Ignore IOAPIC IRQ affinity if possible

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Date:	Mon, 11 Jun 2012 22:41:17 +0300
From:	Ido Yariv <ido@...ery.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	hpa@...or.com, linux-kernel@...r.kernel.org, shai@...lemp.com,
	kiran.thirumalai@...il.com, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org,
	Fengguang Wu <wfg@...ux.intel.com>
Subject: Re: [tip:x86/platform] x86/vsmp: Ignore IOAPIC IRQ affinity if
 possible

Hi Ingo,

On Mon, Jun 11, 2012 at 10:58:43AM +0200, Ingo Molnar wrote:
> 
> * Ido Yariv <ido@...ery.com> wrote:
> 
> > This seems to break when CONFIG_PARAVIRT is set but CONFIG_SMP 
> > isn't. Since there's little point in optimizing IOAPIC routing 
> > for UP kernels, how about the following fix?
> 
> Looks good to me, I'll give it some testing.

I'm afraid this patch is missing one more config dependency. Since
no_irq_affinity is declared in proc.c, we need to verify that
CONFIG_PROC_FS is set before referencing this variable. The below patch
fixes this.

Thanks to Fengguang Wu for reporting this.

Thanks,
Ido.

>From 2a865725447a84a7e3921b01b3683b665e896971 Mon Sep 17 00:00:00 2001
From: Ravikiran Thirumalai <kiran.thirumalai@...il.com>
Date: Sun, 3 Jun 2012 01:11:35 +0300
Subject: [PATCH] x86/vsmp: Ignore IOAPIC IRQ affinity if possible

vSMP can route interrupts more optimally based on internal
knowledge the OS does not have. In order to support this
optimization, all CPUs must be able to handle all possible
IOAPIC interrupts.

Fix this by setting the vector allocation domain for all CPUs
and by enabling this feature in vSMP.

Signed-off-by: Ravikiran Thirumalai <kiran.thirumalai@...il.com>
Signed-off-by: Shai Fultheim <shai@...lemp.com>
[ido@...ery.com: rebased, simplified, and reworded the commit message]
Signed-off-by: Ido Yariv <ido@...ery.com>
---
 arch/x86/kernel/vsmp_64.c |   30 ++++++++++++++++++++++++++----
 1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/vsmp_64.c b/arch/x86/kernel/vsmp_64.c
index 59eea85..3f0285a 100644
--- a/arch/x86/kernel/vsmp_64.c
+++ b/arch/x86/kernel/vsmp_64.c
@@ -16,6 +16,7 @@
 #include <linux/pci_ids.h>
 #include <linux/pci_regs.h>
 #include <linux/smp.h>
+#include <linux/irq.h>
 
 #include <asm/apic.h>
 #include <asm/pci-direct.h>
@@ -95,6 +96,18 @@ static void __init set_vsmp_pv_ops(void)
 	ctl = readl(address + 4);
 	printk(KERN_INFO "vSMP CTL: capabilities:0x%08x  control:0x%08x\n",
 	       cap, ctl);
+
+	/* If possible, let the vSMP foundation route the interrupt optimally */
+#ifdef CONFIG_SMP
+	if (cap & ctl & BIT(8)) {
+		ctl &= ~BIT(8);
+#ifdef CONFIG_PROC_FS
+		/* Don't let users change irq affinity via procfs */
+		no_irq_affinity = 1;
+#endif
+	}
+#endif
+
 	if (cap & ctl & (1 << 4)) {
 		/* Setup irq ops and turn on vSMP  IRQ fastpath handling */
 		pv_irq_ops.irq_disable = PV_CALLEE_SAVE(vsmp_irq_disable);
@@ -102,12 +115,11 @@ static void __init set_vsmp_pv_ops(void)
 		pv_irq_ops.save_fl  = PV_CALLEE_SAVE(vsmp_save_fl);
 		pv_irq_ops.restore_fl  = PV_CALLEE_SAVE(vsmp_restore_fl);
 		pv_init_ops.patch = vsmp_patch;
-
 		ctl &= ~(1 << 4);
-		writel(ctl, address + 4);
-		ctl = readl(address + 4);
-		printk(KERN_INFO "vSMP CTL: control set to:0x%08x\n", ctl);
 	}
+	writel(ctl, address + 4);
+	ctl = readl(address + 4);
+	pr_info("vSMP CTL: control set to:0x%08x\n", ctl);
 
 	early_iounmap(address, 8);
 }
@@ -192,10 +204,20 @@ static int apicid_phys_pkg_id(int initial_apic_id, int index_msb)
 	return hard_smp_processor_id() >> index_msb;
 }
 
+/*
+ * In vSMP, all cpus should be capable of handling interrupts, regardless of
+ * the APIC used.
+ */
+static void fill_vector_allocation_domain(int cpu, struct cpumask *retmask)
+{
+	cpumask_setall(retmask);
+}
+
 static void vsmp_apic_post_init(void)
 {
 	/* need to update phys_pkg_id */
 	apic->phys_pkg_id = apicid_phys_pkg_id;
+	apic->vector_allocation_domain = fill_vector_allocation_domain;
 }
 
 void __init vsmp_init(void)
-- 
1.7.10.2

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