From patchwork Thu Oct 21 18:25:52 2010 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [6/7] kvm: writeback SMP TSCs on migration only Date: Thu, 21 Oct 2010 08:25:52 -0000 From: Marcelo Tosatti X-Patchwork-Id: 68766 Message-Id: <384331a61a8ca42f32516ced20cb52470c5f6f57.1287685553.git.mtosatti@redhat.com> To: Anthony Liguori Cc: Marcelo Tosatti , qemu-devel@nongnu.org, kvm@vger.kernel.org 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 --- target-i386/kvm.c | 10 +++++++++- 1 files changed, 9 insertions(+), 1 deletions(-) diff --git a/target-i386/kvm.c b/target-i386/kvm.c index 06474d6..e2f7e2e 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);