From: Yang Zhang <yang.zhang...@gmail.com>
using smart idle poll to reduce the useless poll when system is idle.
Signed-off-by: Quan Xu <quan....@gmail.com>
Signed-off-by: Yang Zhang <yang.zhang...@gmail.com>
Cc: Paolo Bonzini <pbonz...@redhat.com>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Ingo Molnar <mi...@redhat.com>
Cc: "H. Peter Anvin" <h...@zytor.com>
Cc: x...@kernel.org
Cc: k...@vger.kernel.org
Cc: linux-ker...@vger.kernel.org
---
arch/x86/kernel/kvm.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 47 insertions(+), 0 deletions(-)
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 2a6e402..8bb6d55 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -37,6 +37,7 @@
#include <linux/debugfs.h>
#include <linux/nmi.h>
#include <linux/swait.h>
+#include <linux/tick.h>
#include <asm/timer.h>
#include <asm/cpu.h>
#include <asm/traps.h>
@@ -365,11 +366,57 @@ static void kvm_guest_cpu_init(void)
kvm_register_steal_time();
}
+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 void kvm_idle_update_poll_duration(ktime_t idle)
+{
+ unsigned long poll_duration = this_cpu_read(poll_duration_ns);
+
+ /* so far poll duration is based on nohz */
+ if (idle == -1ULL)
+ return;
+
+ if (poll_duration && idle > paravirt_poll_threshold_ns)
+ poll_duration = shrink_poll_ns(poll_duration,
+ paravirt_poll_shrink);
+ else if (poll_duration < paravirt_poll_threshold_ns &&
+ idle < paravirt_poll_threshold_ns)
+ poll_duration = grow_poll_ns(poll_duration, paravirt_poll_grow,
+ paravirt_poll_threshold_ns);
+
+ this_cpu_write(poll_duration_ns, poll_duration);
+}
+
static void kvm_idle_poll(void)
{
unsigned long poll_duration = this_cpu_read(poll_duration_ns);
+ ktime_t idle = tick_nohz_get_last_idle_length();
ktime_t start, cur, stop;
+ kvm_idle_update_poll_duration(idle);
+
start = cur = ktime_get();
stop = ktime_add_ns(ktime_get(), poll_duration);
--
1.7.1
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