halt_poll_ns_shrink/ |
halt_poll_ns_grow | grow halt_poll_ns | shrink halt_poll_ns
---------------------+----------------------+-------------------
< 1 | = halt_poll_ns | = 0
< halt_poll_ns | *= halt_poll_ns_grow | /= halt_poll_ns_shrink
otherwise | += halt_poll_ns_grow | -= halt_poll_ns_shrink
I was curious why you went with this approach rather than just the
middle row, or just the last row. Do you think we'll want the extra
flexibility?
Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
---
virt/kvm/kvm_main.c | 65
++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 64 insertions(+), 1 deletion(-)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 93db833..2a4962b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -66,9 +66,26 @@
MODULE_AUTHOR("Qumranet");
MODULE_LICENSE("GPL");
-static unsigned int halt_poll_ns;
+#define KVM_HALT_POLL_NS 500000
+#define KVM_HALT_POLL_NS_GROW 2
+#define KVM_HALT_POLL_NS_SHRINK 0
+#define KVM_HALT_POLL_NS_MAX 2000000
The macros are not necessary. Also, hard coding the numbers in the param
definitions will make reading the comments above them easier.
+
+static unsigned int halt_poll_ns = KVM_HALT_POLL_NS;
module_param(halt_poll_ns, uint, S_IRUGO | S_IWUSR);
+/* Default doubles per-vcpu halt_poll_ns. */
+static unsigned int halt_poll_ns_grow = KVM_HALT_POLL_NS_GROW;
+module_param(halt_poll_ns_grow, int, S_IRUGO);
+
+/* Default resets per-vcpu halt_poll_ns . */
+static unsigned int halt_poll_ns_shrink = KVM_HALT_POLL_NS_SHRINK;
+module_param(halt_poll_ns_shrink, int, S_IRUGO);
+
+/* halt polling only reduces halt latency by 10-15 us, 2ms is enough */
Ah, I misspoke before. I was thinking about round-trip latency. The
latency
of a single halt is reduced by about 5-7 us.
+static unsigned int halt_poll_ns_max = KVM_HALT_POLL_NS_MAX;
+module_param(halt_poll_ns_max, int, S_IRUGO);
We can remove halt_poll_ns_max. vcpu->halt_poll_ns can always start at
zero
and grow from there. Then we just need one module param to keep
vcpu->halt_poll_ns from growing too large.
[ It would make more sense to remove halt_poll_ns and keep
halt_poll_ns_max,
but since halt_poll_ns already exists in upstream kernels, we probably
can't
remove it. ]
+
/*
* Ordering of locks:
*
@@ -1907,6 +1924,48 @@ void kvm_vcpu_mark_page_dirty(struct kvm_vcpu
*vcpu, gfn_t gfn)
}
EXPORT_SYMBOL_GPL(kvm_vcpu_mark_page_dirty);
+static unsigned int __grow_halt_poll_ns(unsigned int val)
+{
+ if (halt_poll_ns_grow < 1)
+ return halt_poll_ns;
+
+ val = min(val, halt_poll_ns_max);
+
+ if (val == 0)
+ return halt_poll_ns;
+
+ if (halt_poll_ns_grow < halt_poll_ns)
+ val *= halt_poll_ns_grow;
+ else
+ val += halt_poll_ns_grow;
+
+ return val;
+}
+
+static unsigned int __shrink_halt_poll_ns(int val, int modifier, int
minimum)
minimum never gets used.
+{
+ if (modifier < 1)
+ return 0;
+
+ if (modifier < halt_poll_ns)
+ val /= modifier;
+ else
+ val -= modifier;
+
+ return val;
+}
+
+static void grow_halt_poll_ns(struct kvm_vcpu *vcpu)
These wrappers aren't necessary.
+{
+ vcpu->halt_poll_ns = __grow_halt_poll_ns(vcpu->halt_poll_ns);
+}
+
+static void shrink_halt_poll_ns(struct kvm_vcpu *vcpu)
+{
+ vcpu->halt_poll_ns = __shrink_halt_poll_ns(vcpu->halt_poll_ns,
+ halt_poll_ns_shrink, halt_poll_ns);
+}
+
static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)
{
if (kvm_arch_vcpu_runnable(vcpu)) {
@@ -1954,6 +2013,10 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
break;
waited = true;
+ if (vcpu->halt_poll_ns > halt_poll_ns_max)
+ shrink_halt_poll_ns(vcpu);
+ else
+ grow_halt_poll_ns(vcpu);
Shouldn't this go after the loop, and before "out:", in case we schedule
more than once? You can gate it on "if (waited)" so it only runs if we
actually scheduled.
schedule();
}
--
1.9.1
