[Devel] [PATCH RHEL7 COMMIT] ms/kvm: halt_polling: improve grow/shrink settings

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-327.10.1.vz7.12.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-327.10.1.vz7.12.11
------>
commit 22631bc0045bcd5c83233b3c3194bc49d7681d78
Author: Christian Borntraeger <borntraeger at de.ibm.com>
Date:   Tue Apr 19 14:22:52 2016 +0400

    ms/kvm: halt_polling: improve grow/shrink settings
    
    Right now halt_poll_ns can be change during runtime. The
    grow and shrink factors can only be set during module load.
    Lets fix several aspects of grow shrink:
    - make grow/shrink changeable by root
    - make all variables unsigned int
    - read the variables once to prevent races
    
    Signed-off-by: Christian Borntraeger <borntraeger at de.ibm.com>
    Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
    (cherry picked from commit 6b6de68c63eda6240ec92e44b998f910156f8806)
    
    Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov at virtuozzo.com>
---
 include/trace/events/kvm.h |  9 +++++----
 virt/kvm/kvm_main.c        | 18 ++++++++++--------
 2 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/include/trace/events/kvm.h b/include/trace/events/kvm.h
index 45afe07..4c05352 100644
--- a/include/trace/events/kvm.h
+++ b/include/trace/events/kvm.h
@@ -355,14 +355,15 @@ TRACE_EVENT(
 );
 
 TRACE_EVENT(kvm_halt_poll_ns,
-	TP_PROTO(bool grow, unsigned int vcpu_id, int new, int old),
+	TP_PROTO(bool grow, unsigned int vcpu_id, unsigned int new,
+		 unsigned int old),
 	TP_ARGS(grow, vcpu_id, new, old),
 
 	TP_STRUCT__entry(
 		__field(bool, grow)
 		__field(unsigned int, vcpu_id)
-		__field(int, new)
-		__field(int, old)
+		__field(unsigned int, new)
+		__field(unsigned int, old)
 	),
 
 	TP_fast_assign(
@@ -372,7 +373,7 @@ TRACE_EVENT(kvm_halt_poll_ns,
 		__entry->old            = old;
 	),
 
-	TP_printk("vcpu %u: halt_poll_ns %d (%s %d)",
+	TP_printk("vcpu %u: halt_poll_ns %u (%s %u)",
 			__entry->vcpu_id,
 			__entry->new,
 			__entry->grow ? "grow" : "shrink",
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 870c968..4cbac86 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -72,11 +72,11 @@ module_param(halt_poll_ns, uint, S_IRUGO | S_IWUSR);
 
 /* Default doubles per-vcpu halt_poll_ns. */
 static unsigned int halt_poll_ns_grow = 2;
-module_param(halt_poll_ns_grow, int, S_IRUGO);
+module_param(halt_poll_ns_grow, uint, S_IRUGO | S_IWUSR);
 
 /* Default resets per-vcpu halt_poll_ns . */
 static unsigned int halt_poll_ns_shrink;
-module_param(halt_poll_ns_shrink, int, S_IRUGO);
+module_param(halt_poll_ns_shrink, uint, S_IRUGO | S_IWUSR);
 
 /*
  * Ordering of locks:
@@ -1945,14 +1945,15 @@ EXPORT_SYMBOL_GPL(kvm_vcpu_mark_page_dirty);
 
 static void grow_halt_poll_ns(struct kvm_vcpu *vcpu)
 {
-	int old, val;
+	unsigned int old, val, grow;
 
 	old = val = vcpu->halt_poll_ns;
+	grow = READ_ONCE(halt_poll_ns_grow);
 	/* 10us base */
-	if (val == 0 && halt_poll_ns_grow)
+	if (val == 0 && grow)
 		val = 10000;
 	else
-		val *= halt_poll_ns_grow;
+		val *= grow;
 
 	vcpu->halt_poll_ns = val;
 	trace_kvm_halt_poll_ns_grow(vcpu->vcpu_id, val, old);
@@ -1960,13 +1961,14 @@ static void grow_halt_poll_ns(struct kvm_vcpu *vcpu)
 
 static void shrink_halt_poll_ns(struct kvm_vcpu *vcpu)
 {
-	int old, val;
+	unsigned int old, val, shrink;
 
 	old = val = vcpu->halt_poll_ns;
-	if (halt_poll_ns_shrink == 0)
+	shrink = READ_ONCE(halt_poll_ns_shrink);
+	if (shrink == 0)
 		val = 0;
 	else
-		val /= halt_poll_ns_shrink;
+		val /= shrink;
 
 	vcpu->halt_poll_ns = val;
 	trace_kvm_halt_poll_ns_shrink(vcpu->vcpu_id, val, old);