[RFC PATCH v2 6/7] KVM guest: introduce smart idle poll algorithm

Yang Zhang
2017-08-29T11:48:19Z

using smart idle poll to reduce the useless poll when system is idle.

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: 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 | 41 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 41 insertions(+)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 7d84a02..ffc8307 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -373,12 +373,53 @@ static void kvm_idle_poll(void)
} while (ktime_before(cur, stop));
}

+static unsigned int grow_poll_ns(unsigned int old, unsigned int grow,
+ unsigned int max)
+{
+ unsigned int val;
+
+ /* set base poll time to 10000ns */
+ if (old == 0 && grow)
+ return 10000;
+
+ val = old * grow;
+ if (val > max)
+ val = max;
+
+ return val;
+}
+
+static unsigned int shrink_poll_ns(unsigned int old, unsigned int shrink)
+{
+ if (shrink == 0)
+ return 0;
+
+ return old / shrink;
+}
+
+static int kvm_idle_update_poll_duration(unsigned long idle_duration)
+{
+ unsigned long poll_duration = this_cpu_read(poll_duration_ns);
+
+ if (poll_duration && idle_duration > poll_threshold_ns)
+ poll_duration = shrink_poll_ns(poll_duration, poll_shrink);
+ else if (poll_duration < poll_threshold_ns &&
+ idle_duration < poll_threshold_ns)
+ poll_duration = grow_poll_ns(poll_duration, poll_grow,
+ poll_threshold_ns);
+
+ this_cpu_write(poll_duration_ns, poll_duration);
+
+ return 0;
+}
+
static void kvm_guest_idle_init(void)
{
if (!kvm_para_available())
return;

pv_idle_ops.poll = kvm_idle_poll;
+ pv_idle_ops.update = kvm_idle_update_poll_duration;
}

static void kvm_pv_disable_apf(void)
--
1.8.3.1