[patch 0/2] use smp_send_reschedule in kvm_vcpu_kick (v3)

[patch 0/2] use smp_send_reschedule in kvm_vcpu_kick (v3)

[Marcelo Tosatti]

This is needed to fix
http://www.mail-archive.com/kvm@vger.kernel.org/msg11004.html
with the added benefit of collapsing IPI's.

- Export smp_send_reschedule on IA64 as requested by Xiantao Zhang.
- Possible to use workqueue on compat code (< 2.6.24).


-- 

[patch 1/2] IA64: export smp_send_reschedule

[Marcelo Tosatti]

[-- Attachment #1: export-smp-send-resched-on-ia64 --]
[-- Type: text/plain, Size: 521 bytes --]

To be used by KVM.

CC: <xiantao.zhang@intel.com>
CC: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

Index: kvm/arch/ia64/kernel/smp.c
===================================================================
--- kvm.orig/arch/ia64/kernel/smp.c
+++ kvm/arch/ia64/kernel/smp.c
@@ -225,6 +225,7 @@ smp_send_reschedule (int cpu)
 {
 	platform_send_ipi(cpu, IA64_IPI_RESCHEDULE, IA64_IPI_DM_INT, 0);
 }
+EXPORT_SYMBOL_GPL(smp_send_reschedule);
 
 /*
  * Called with preemption disabled.

-- 

[patch 2/2] KVM: use smp_send_reschedule in kvm_vcpu_kick

[Marcelo Tosatti]

[-- Attachment #1: smp-send-resch --]
[-- Type: text/plain, Size: 5391 bytes --]

KVM uses a function call IPI to cause the exit of a guest running on a
physical cpu. For virtual interrupt notification there is no need to
wait on IPI receival, or to execute any function.

This is exactly what the reschedule IPI does, without the overhead
of function IPI. So use it instead of smp_call_function_single in
kvm_vcpu_kick.

Also change the "guest_mode" variable to a bit in vcpu->requests, and
use that to collapse multiple IPI's that would be issued between the
first one and zeroing of guest mode.

This allows kvm_vcpu_kick to called with interrupts disabled.

Untested on IA64.

CC: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

Index: kvm/arch/ia64/kernel/irq_ia64.c
===================================================================
--- kvm.orig/arch/ia64/kernel/irq_ia64.c
+++ kvm/arch/ia64/kernel/irq_ia64.c
@@ -610,6 +610,9 @@ static struct irqaction ipi_irqaction = 
 	.name =		"IPI"
 };
 
+/*
+ * KVM uses this interrupt to force a cpu out of guest mode
+ */
 static struct irqaction resched_irqaction = {
 	.handler =	dummy_handler,
 	.flags =	IRQF_DISABLED,
Index: kvm/arch/ia64/kvm/kvm-ia64.c
===================================================================
--- kvm.orig/arch/ia64/kvm/kvm-ia64.c
+++ kvm/arch/ia64/kvm/kvm-ia64.c
@@ -673,7 +673,7 @@ again:
 		goto out;
 	}
 
-	vcpu->guest_mode = 1;
+	clear_bit(KVM_REQ_KICK, &vcpu->requests);
 	kvm_guest_enter();
 	down_read(&vcpu->kvm->slots_lock);
 	r = vti_vcpu_run(vcpu, kvm_run);
@@ -685,7 +685,7 @@ again:
 	}
 
 	vcpu->arch.launched = 1;
-	vcpu->guest_mode = 0;
+	set_bit(KVM_REQ_KICK, &vcpu->requests);
 	local_irq_enable();
 
 	/*
@@ -1875,24 +1875,17 @@ void kvm_arch_hardware_unsetup(void)
 {
 }
 
-static void vcpu_kick_intr(void *info)
-{
-#ifdef DEBUG
-	struct kvm_vcpu *vcpu = (struct kvm_vcpu *)info;
-	printk(KERN_DEBUG"vcpu_kick_intr %p \n", vcpu);
-#endif
-}
-
 void kvm_vcpu_kick(struct kvm_vcpu *vcpu)
 {
-	int ipi_pcpu = vcpu->cpu;
-	int cpu = get_cpu();
+	int me = get_cpu();
+	int cpu = vcpu->cpu;
 
 	if (waitqueue_active(&vcpu->wq))
 		wake_up_interruptible(&vcpu->wq);
 
-	if (vcpu->guest_mode && cpu != ipi_pcpu)
-		smp_call_function_single(ipi_pcpu, vcpu_kick_intr, vcpu, 0);
+	if (cpu != me && (unsigned) cpu < nr_cpu_ids && cpu_online(cpu))
+		if (!test_and_set_bit(KVM_REQ_KICK, &vcpu->requests))
+			smp_send_reschedule(cpu);
 	put_cpu();
 }
 
Index: kvm/arch/x86/kernel/smp.c
===================================================================
--- kvm.orig/arch/x86/kernel/smp.c
+++ kvm/arch/x86/kernel/smp.c
@@ -172,6 +172,9 @@ void smp_reschedule_interrupt(struct pt_
 {
 	ack_APIC_irq();
 	inc_irq_stat(irq_resched_count);
+	/*
+	 * KVM uses this interrupt to force a cpu out of guest mode
+	 */
 }
 
 void smp_call_function_interrupt(struct pt_regs *regs)
Index: kvm/arch/x86/kvm/x86.c
===================================================================
--- kvm.orig/arch/x86/kvm/x86.c
+++ kvm/arch/x86/kvm/x86.c
@@ -3146,6 +3146,9 @@ static int vcpu_enter_guest(struct kvm_v
 
 	local_irq_disable();
 
+	clear_bit(KVM_REQ_KICK, &vcpu->requests);
+	smp_mb__after_clear_bit();
+
 	if (vcpu->requests || need_resched() || signal_pending(current)) {
 		local_irq_enable();
 		preempt_enable();
@@ -3153,13 +3156,6 @@ static int vcpu_enter_guest(struct kvm_v
 		goto out;
 	}
 
-	vcpu->guest_mode = 1;
-	/*
-	 * Make sure that guest_mode assignment won't happen after
-	 * testing the pending IRQ vector bitmap.
-	 */
-	smp_wmb();
-
 	if (vcpu->arch.exception.pending)
 		__queue_exception(vcpu);
 	else if (irqchip_in_kernel(vcpu->kvm))
@@ -3201,7 +3197,7 @@ static int vcpu_enter_guest(struct kvm_v
 	set_debugreg(vcpu->arch.host_dr6, 6);
 	set_debugreg(vcpu->arch.host_dr7, 7);
 
-	vcpu->guest_mode = 0;
+	set_bit(KVM_REQ_KICK, &vcpu->requests);
 	local_irq_enable();
 
 	++vcpu->stat.exits;
@@ -4483,29 +4479,20 @@ int kvm_arch_vcpu_runnable(struct kvm_vc
 	       || vcpu->arch.nmi_pending;
 }
 
-static void vcpu_kick_intr(void *info)
-{
-#ifdef DEBUG
-	struct kvm_vcpu *vcpu = (struct kvm_vcpu *)info;
-	printk(KERN_DEBUG "vcpu_kick_intr %p \n", vcpu);
-#endif
-}
-
 void kvm_vcpu_kick(struct kvm_vcpu *vcpu)
 {
-	int ipi_pcpu = vcpu->cpu;
-	int cpu = get_cpu();
+	int me = get_cpu();
+	int cpu = vcpu->cpu;
 
 	if (waitqueue_active(&vcpu->wq)) {
 		wake_up_interruptible(&vcpu->wq);
 		++vcpu->stat.halt_wakeup;
 	}
-	/*
-	 * We may be called synchronously with irqs disabled in guest mode,
-	 * So need not to call smp_call_function_single() in that case.
-	 */
-	if (vcpu->guest_mode && vcpu->cpu != cpu)
-		smp_call_function_single(ipi_pcpu, vcpu_kick_intr, vcpu, 0);
+
+	if (cpu != me && (unsigned)cpu < nr_cpu_ids && cpu_online(cpu))
+		if (!test_and_set_bit(KVM_REQ_KICK, &vcpu->requests))
+			smp_send_reschedule(cpu);
+
 	put_cpu();
 }
 
Index: kvm/include/linux/kvm_host.h
===================================================================
--- kvm.orig/include/linux/kvm_host.h
+++ kvm/include/linux/kvm_host.h
@@ -38,6 +38,7 @@
 #define KVM_REQ_UNHALT             6
 #define KVM_REQ_MMU_SYNC           7
 #define KVM_REQ_KVMCLOCK_UPDATE    8
+#define KVM_REQ_KICK               9
 
 #define KVM_USERSPACE_IRQ_SOURCE_ID	0
 
@@ -72,7 +73,6 @@ struct kvm_vcpu {
 	struct mutex mutex;
 	int   cpu;
 	struct kvm_run *run;
-	int guest_mode;
 	unsigned long requests;
 	unsigned long guest_debug;
 	int fpu_active;

-- 

RE: [patch 1/2] IA64: export smp_send_reschedule

[Zhang, Xiantao]

Hi, Tony
	Could you help to ack the patch ? 
Xiantao

Acked-by: Xiantao Zhang <xiantao.zhang@intel.com>



Marcelo Tosatti wrote:
> To be used by KVM.
> 
> CC: <xiantao.zhang@intel.com>
> CC: Gleb Natapov <gleb@redhat.com>
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> 
> Index: kvm/arch/ia64/kernel/smp.c
> ===================================================================
> --- kvm.orig/arch/ia64/kernel/smp.c
> +++ kvm/arch/ia64/kernel/smp.c
> @@ -225,6 +225,7 @@ smp_send_reschedule (int cpu)
>  {
>  	platform_send_ipi(cpu, IA64_IPI_RESCHEDULE, IA64_IPI_DM_INT, 0);
>  }
> +EXPORT_SYMBOL_GPL(smp_send_reschedule);
> 
>  /*
>   * Called with preemption disabled.

RE: [patch 1/2] IA64: export smp_send_reschedule

[Luck, Tony]

I could do more than Ack it, I could apply it (since it is
in arch/ia64.  But "To be used by KVM" is a bit vague for
a commit description.  A bit more detail please.

-Tony

-----Original Message-----
From: Zhang, Xiantao
Sent: Monday, April 13, 2009 6:57 PM
To: Marcelo Tosatti; kvm@vger.kernel.org; Luck, Tony
Cc: Gleb Natapov
Subject: RE: [patch 1/2] IA64: export smp_send_reschedule

Hi, Tony
        Could you help to ack the patch ?
Xiantao

Acked-by: Xiantao Zhang <xiantao.zhang@intel.com>



Marcelo Tosatti wrote:
> To be used by KVM.
>
> CC: <xiantao.zhang@intel.com>
> CC: Gleb Natapov <gleb@redhat.com>
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
>
> Index: kvm/arch/ia64/kernel/smp.c
> ===================================================================
> --- kvm.orig/arch/ia64/kernel/smp.c
> +++ kvm/arch/ia64/kernel/smp.c
> @@ -225,6 +225,7 @@ smp_send_reschedule (int cpu)
>  {
>       platform_send_ipi(cpu, IA64_IPI_RESCHEDULE, IA64_IPI_DM_INT, 0);
>  }
> +EXPORT_SYMBOL_GPL(smp_send_reschedule);
>
>  /*
>   * Called with preemption disabled.

IA64: export smp_send_reschedule

[Marcelo Tosatti]

KVM will use smp_send_reschedule to force a cpu out of guest mode.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

Index: kvm/arch/ia64/kernel/smp.c
===================================================================
--- kvm.orig/arch/ia64/kernel/smp.c
+++ kvm/arch/ia64/kernel/smp.c
@@ -225,6 +225,7 @@ smp_send_reschedule (int cpu)
 {
 	platform_send_ipi(cpu, IA64_IPI_RESCHEDULE, IA64_IPI_DM_INT, 0);
 }
+EXPORT_SYMBOL_GPL(smp_send_reschedule);
 
 /*
  * Called with preemption disabled.