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kvmclock: add a new function to update env->tsc.

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The commit 317b0a6d8 fixed an issue which caused by the outdated
env->tsc value, but the fix lead to 'cpu_synchronize_all_states()'
called twice during live migration. The 'cpu_synchronize_all_states()'
takes about 130us for a VM which has 4 vcpus, it's a bit expensive.

Synchronize the whole CPU context just for updating env->tsc is too
wasting, this patch use a new function to update the env->tsc.
Comparing to 'cpu_synchronize_all_states()', it only takes about 20us.

Signed-off-by: Liang Li <liang.z.li@intel.com>
Message-Id: <1446695464-27116-2-git-send-email-liang.z.li@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Liang Li 2015-11-05 11:51:03 +08:00 • committed by Paolo Bonzini
parent b553a04280
commit 0fd7e098db
3 changed files with 48 additions and 16 deletions
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18
hw/i386/kvm/clock.c
View file

@ -17,7 +17,7 @@
#include "qemu/host-utils.h"
#include "sysemu/sysemu.h"
#include "sysemu/kvm.h"
#include "sysemu/cpus.h"
#include "kvm_i386.h"
#include "hw/sysbus.h"
#include "hw/kvm/clock.h"
@ -125,21 +125,7 @@ static void kvmclock_vm_state_change(void *opaque, int running,
return;
}
cpu_synchronize_all_states();
/* In theory, the cpu_synchronize_all_states() call above wouldn't
* affect the rest of the code, as the VCPU state inside CPUState
* is supposed to always match the VCPU state on the kernel side.
*
* In practice, calling cpu_synchronize_state() too soon will load the
* kernel-side APIC state into X86CPU.apic_state too early, APIC state
* won't be reloaded later because CPUState.vcpu_dirty==true, and
* outdated APIC state may be migrated to another host.
*
* The real fix would be to make sure outdated APIC state is read
* from the kernel again when necessary. While this is not fixed, we
* need the cpu_clean_all_dirty() call below.
*/
cpu_clean_all_dirty();
kvm_synchronize_all_tsc();
ret = kvm_vm_ioctl(kvm_state, KVM_GET_CLOCK, &data);
if (ret < 0) {