Patchwork [v2,2/2] make kvmclock value idempotent for stopped machine

login
register
mail settings
Submitter Glauber Costa
Date Dec. 6, 2010, 2:03 p.m.
Message ID <1291644227-22923-3-git-send-email-glommer@redhat.com>
Download mbox | patch
Permalink /patch/74360/
State New
Headers show

Comments

Glauber Costa - Dec. 6, 2010, 2:03 p.m.
Although we never made such commitment clear (well, to the best
of my knowledge), some people expect that two savevm issued in sequence
in a stopped machine will yield the same results. This is not a crazy
requirement, since we don't expect a stopped machine to be updating its state,
for any device.

With kvmclock, this is not the case, since the .pre_save hook will issue an
ioctl to the host to acquire a timestamp, which is always changing.

This patch moves the value acquisition to vm state change handlers, conditional
on not being run. This could mean mean our get clock ioctl is issued more times,
but this should be fine since vm_stop is not a hot path.

When we do migrate, we'll transfer that value along.

Signed-off-by: Glauber Costa <glommer@redhat.com>
CC: Paolo Bonzini <pbonzini@redhat.com>

---
 qemu-kvm-x86.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

Patch

diff --git a/qemu-kvm-x86.c b/qemu-kvm-x86.c
index 14a52ce..0e357ac 100644
--- a/qemu-kvm-x86.c
+++ b/qemu-kvm-x86.c
@@ -500,11 +500,11 @@  static int kvm_enable_tpr_access_reporting(CPUState *env)
 #ifdef KVM_CAP_ADJUST_CLOCK
 static struct kvm_clock_data kvmclock_data;
 
-static void kvmclock_pre_save(void *opaque)
+static void kvmclock_update_clock(void *opaque, int running, int reason)
 {
     struct kvm_clock_data *cl = opaque;
 
-    if (!kvmclock_enabled)
+    if ((!kvmclock_enabled) || running)
         return;
 
     kvm_vm_ioctl(kvm_state, KVM_GET_CLOCK, cl);
@@ -522,7 +522,6 @@  static const VMStateDescription vmstate_kvmclock= {
     .version_id = 1,
     .minimum_version_id = 1,
     .minimum_version_id_old = 1,
-    .pre_save = kvmclock_pre_save,
     .post_load = kvmclock_post_load,
     .fields      = (VMStateField []) {
         VMSTATE_U64(clock, struct kvm_clock_data),
@@ -537,6 +536,7 @@  void kvmclock_register_savevm(void)
 #ifdef KVM_CAP_ADJUST_CLOCK
     if (kvmclock_enabled && kvm_check_extension(kvm_state, KVM_CAP_ADJUST_CLOCK)) {
         vmstate_register(NULL, 0, &vmstate_kvmclock, &kvmclock_data);
+        qemu_add_vm_change_state_handler(kvmclock_update_clock, &kvmclock_data);
     }
 #endif
 }