linux-kernel - [RFC PATCH v1 1/2] xen/apic: Use vAPIC for IPI if the hardware supports it.

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Date:	Wed,  7 Oct 2015 16:21:49 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	boris.ostrovsky@...cle.com, joao.m.martins@...cle.com,
	david.vrabel@...rix.com, jgross@...e.com,
	dario.faggioli@...rix.com, xen-devel@...ts.xenproject.org,
	linux-kernel@...r.kernel.org
Cc:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: [RFC PATCH v1 1/2] xen/apic: Use vAPIC for IPI if the hardware supports it.

Instead of using the event channels.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
---
 arch/x86/xen/smp.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index 3f4ebf0..d4f4560 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -793,15 +793,33 @@ static int xen_hvm_cpu_up(unsigned int cpu, struct task_struct *tidle)
 	return rc;
 }
 
+static bool __init xen_use_vapic(void)
+{
+	uint32_t eax = cpuid_eax(xen_cpuid_base() + 4);
+
+	if (((eax & XEN_HVM_CPUID_X2APIC_VIRT) && x2apic_mode) ||
+	    ((eax & XEN_HVM_CPUID_APIC_ACCESS_VIRT) && cpu_has_apic))
+		return true;
+
+	return false;
+}
 void __init xen_hvm_smp_init(void)
 {
+	bool vapic;
+
 	if (!xen_have_vector_callback)
 		return;
+
+	vapic = xen_use_vapic();
 	smp_ops.smp_prepare_cpus = xen_hvm_smp_prepare_cpus;
-	smp_ops.smp_send_reschedule = xen_smp_send_reschedule;
 	smp_ops.cpu_up = xen_hvm_cpu_up;
 	smp_ops.cpu_die = xen_cpu_die;
+	smp_ops.smp_prepare_boot_cpu = xen_smp_prepare_boot_cpu;
+
+	printk("Using %s IPI mode\n", vapic ? "vAPIC" : "event channel");
+	if (vapic)
+		return;
+	smp_ops.smp_send_reschedule = xen_smp_send_reschedule;
 	smp_ops.send_call_func_ipi = xen_smp_send_call_function_ipi;
 	smp_ops.send_call_func_single_ipi = xen_smp_send_call_function_single_ipi;
-	smp_ops.smp_prepare_boot_cpu = xen_smp_prepare_boot_cpu;
 }
-- 
2.4.3

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