linux-kernel - [RFC PATCH v2 2/7] KVM guest: register kvm_idle_poll for pv_idle

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Date:   Tue, 29 Aug 2017 11:46:36 +0000
From:   Yang Zhang <yang.zhang.wz@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     kvm@...r.kernel.org, wanpeng.li@...mail.com, mst@...hat.com,
        pbonzini@...hat.com, tglx@...utronix.de, rkrcmar@...hat.com,
        dmatlack@...gle.com, agraf@...e.de, peterz@...radead.org,
        linux-doc@...r.kernel.org, Yang Zhang <yang.zhang.wz@...il.com>,
        Quan Xu <quan.xu0@...il.com>, Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: [RFC PATCH v2 2/7] KVM guest: register kvm_idle_poll for pv_idle_ops

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(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@...il.com>
Signed-off-by: Quan Xu <quan.xu0@...il.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: x86@...nel.org
Cc: kvm@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
---
 arch/x86/kernel/kvm.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index d04e30e..7d84a02 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;
@@ -357,6 +358,29 @@ 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))
@@ -492,6 +516,8 @@ 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
-- 
1.8.3.1