Re: [GIT PULL] x86/apic changes for v4.4

[Linus Torvalds]

On Tue, Nov 3, 2015 at 2:32 AM, Ingo Molnar <mingo@xxxxxxxxxx> wrote:
>
> Please pull the latest x86-apic-for-linus git tree from:

Side note, I have an *old* patch that I think simplifies the
(reasonably common) case of sending IPI's to individual CPU's. That's
done by the "reschedule ipi" in particular.

That's something that is trivially done on the x2apic, but that the
mask-based interfaces makes insanely complicated.

I have *not* rebased this on top of modern kernels so it may not
actually work as a patch any more, because I'm just sending this out
as a "Hmm, what do you guys think" rather than a real submission.

Comments?

                Linus
From 9f09a8b2a1fa58f2e692af4a7283fd1674749d39 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Date: Fri, 20 Feb 2015 11:06:02 -0800
Subject: [PATCH] x86: add a single-target IPI function to the apic

We still fall back on the "send mask" versions if an apic definition
doesn't have the single-target version, but at least this allows the
(trivial) case for the common clustered x2apic case.

Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
---
 arch/x86/include/asm/apic.h           |  1 +
 arch/x86/kernel/apic/x2apic_cluster.c |  9 +++++++++
 arch/x86/kernel/smp.c                 | 16 ++++++++++++++--
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index 92003f3c8a42..5d47ffcfa65d 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -296,6 +296,7 @@ struct apic {
 				      unsigned int *apicid);
 
 	/* ipi */
+	void (*send_IPI)(int cpu, int vector);
 	void (*send_IPI_mask)(const struct cpumask *mask, int vector);
 	void (*send_IPI_mask_allbutself)(const struct cpumask *mask,
 					 int vector);
diff --git a/arch/x86/kernel/apic/x2apic_cluster.c b/arch/x86/kernel/apic/x2apic_cluster.c
index e658f21681c8..177c4fb027a1 100644
--- a/arch/x86/kernel/apic/x2apic_cluster.c
+++ b/arch/x86/kernel/apic/x2apic_cluster.c
@@ -23,6 +23,14 @@ static inline u32 x2apic_cluster(int cpu)
 	return per_cpu(x86_cpu_to_logical_apicid, cpu) >> 16;
 }
 
+static void x2apic_send_IPI(int cpu, int vector)
+{
+	u32 dest = per_cpu(x86_cpu_to_logical_apicid, cpu);
+
+	x2apic_wrmsr_fence();
+	__x2apic_send_IPI_dest(dest, vector, APIC_DEST_LOGICAL);
+}
+
 static void
 __x2apic_send_IPI_mask(const struct cpumask *mask, int vector, int apic_dest)
 {
@@ -266,6 +274,7 @@ static struct apic apic_x2apic_cluster = {
 
 	.cpu_mask_to_apicid_and		= x2apic_cpu_mask_to_apicid_and,
 
+	.send_IPI			= x2apic_send_IPI,
 	.send_IPI_mask			= x2apic_send_IPI_mask,
 	.send_IPI_mask_allbutself	= x2apic_send_IPI_mask_allbutself,
 	.send_IPI_allbutself		= x2apic_send_IPI_allbutself,
diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index be8e1bde07aa..78c9b12d892a 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -114,6 +114,18 @@ static atomic_t stopping_cpu = ATOMIC_INIT(-1);
 static bool smp_no_nmi_ipi = false;
 
 /*
+ * Helper wrapper: not all apic definitions support sending to
+ * a single CPU, so we fall back to sending to a mask.
+ */
+static void send_IPI_cpu(int cpu, int vector)
+{
+	if (apic->send_IPI)
+		apic->send_IPI(cpu, vector);
+	else
+		apic->send_IPI_mask(cpumask_of(cpu), vector);
+}
+
+/*
  * this function sends a 'reschedule' IPI to another CPU.
  * it goes straight through and wastes no time serializing
  * anything. Worst case is that we lose a reschedule ...
@@ -124,12 +136,12 @@ static void native_smp_send_reschedule(int cpu)
 		WARN_ON(1);
 		return;
 	}
-	apic->send_IPI_mask(cpumask_of(cpu), RESCHEDULE_VECTOR);
+	send_IPI_cpu(cpu, RESCHEDULE_VECTOR);
 }
 
 void native_send_call_func_single_ipi(int cpu)
 {
-	apic->send_IPI_mask(cpumask_of(cpu), CALL_FUNCTION_SINGLE_VECTOR);
+	send_IPI_cpu(cpu, CALL_FUNCTION_SINGLE_VECTOR);
 }
 
 void native_send_call_func_ipi(const struct cpumask *mask)
-- 
2.6.2.402.g2635c2b