[PATCH RFC v3 2/6] KVM guest: register kvm_idle_poll for pv_idle_ops

[Quan Xu <quan.xu03@gmail.com>]

From: Quan Xu <quan.xu0@gmail.com>

Although smart idle poll has nothing to do with paravirt, it can
not bring any benifit to native. So we only enable it when Linux
runs as a KVM guest( also it can extend to other hypervisor like
Xen, HyperV and VMware).

Introduce per-CPU variable poll_duration_ns to control the max
poll time.

Signed-off-by: Yang Zhang <yang.zhang.wz@gmail.com>
Signed-off-by: Quan Xu <quan.xu0@gmail.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: kvm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
 arch/x86/kernel/kvm.c |   26 ++++++++++++++++++++++++++
 1 files changed, 26 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 8bb9594..2a6e402 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -75,6 +75,7 @@ static int parse_no_kvmclock_vsyscall(char *arg)
 
 early_param("no-kvmclock-vsyscall", parse_no_kvmclock_vsyscall);
 
+static DEFINE_PER_CPU(unsigned long, poll_duration_ns);
 static DEFINE_PER_CPU(struct kvm_vcpu_pv_apf_data, apf_reason) __aligned(64);
 static DEFINE_PER_CPU(struct kvm_steal_time, steal_time) __aligned(64);
 static int has_steal_clock = 0;
@@ -364,6 +365,29 @@ static void kvm_guest_cpu_init(void)
 		kvm_register_steal_time();
 }
 
+static void kvm_idle_poll(void)
+{
+	unsigned long poll_duration = this_cpu_read(poll_duration_ns);
+	ktime_t start, cur, stop;
+
+	start = cur = ktime_get();
+	stop = ktime_add_ns(ktime_get(), poll_duration);
+
+	do {
+		if (need_resched())
+			break;
+		cur = ktime_get();
+	} while (ktime_before(cur, stop));
+}
+
+static void kvm_guest_idle_init(void)
+{
+	if (!kvm_para_available())
+		return;
+
+	pv_idle_ops.poll = kvm_idle_poll;
+}
+
 static void kvm_pv_disable_apf(void)
 {
 	if (!__this_cpu_read(apf_reason.enabled))
@@ -499,6 +523,8 @@ void __init kvm_guest_init(void)
 	kvm_guest_cpu_init();
 #endif
 
+	kvm_guest_idle_init();
+
 	/*
 	 * Hard lockup detection is enabled by default. Disable it, as guests
 	 * can get false positives too easily, for example if the host is
-- 
1.7.1


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