From: Marcelo Tosatti Date: Thu, 21 Oct 2010 15:35:03 +0000 (-0200) Subject: kvm: writeback SMP TSCs on migration only X-Git-Tag: qemu-xen-4.2.0~2165^2~1 X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=384331a61a8ca42f32516ced20cb52470c5f6f57;p=qemu-upstream-4.2-testing.git kvm: writeback SMP TSCs on migration only commit 6389c45441269baa2873e6feafebd17105ddeaf6 Author: Jan Kiszka Date: Mon Mar 1 18:17:26 2010 +0100 qemu-kvm: Cleanup/fix TSC and PV clock writeback Signed-off-by: Marcelo Tosatti --- diff --git a/target-i386/kvm.c b/target-i386/kvm.c index 06474d616..e2f7e2ef4 100644 --- a/target-i386/kvm.c +++ b/target-i386/kvm.c @@ -817,7 +817,15 @@ static int kvm_put_msrs(CPUState *env, int level) kvm_msr_entry_set(&msrs[n++], MSR_LSTAR, env->lstar); #endif if (level == KVM_PUT_FULL_STATE) { - kvm_msr_entry_set(&msrs[n++], MSR_IA32_TSC, env->tsc); + /* + * KVM is yet unable to synchronize TSC values of multiple VCPUs on + * writeback. Until this is fixed, we only write the offset to SMP + * guests after migration, desynchronizing the VCPUs, but avoiding + * huge jump-backs that would occur without any writeback at all. + */ + if (smp_cpus == 1 || env->tsc != 0) { + kvm_msr_entry_set(&msrs[n++], MSR_IA32_TSC, env->tsc); + } kvm_msr_entry_set(&msrs[n++], MSR_KVM_SYSTEM_TIME, env->system_time_msr); kvm_msr_entry_set(&msrs[n++], MSR_KVM_WALL_CLOCK, env->wall_clock_msr);