On Tue, Nov 24, 2015 at 11:33:57AM +0800, Haozhong Zhang wrote:
> This patch enables migrating vcpu's TSC rate. If KVM on the destination
> machine supports TSC scaling, guest programs will observe a consistent
> TSC rate across the migration.
>
> If TSC scaling is not supported on the destination machine, the
> migration will not be aborted and QEMU on the destination will not set
> vcpu's TSC rate to the migrated value.
>
> If vcpu's TSC rate specified by CPU option 'tsc-freq' on the destination
> machine is inconsistent with the migrated TSC rate, the migration will
> be aborted.
>
> For backwards compatibility, the migration of vcpu's TSC rate is
> disabled on pc-*-2.4 and older machine types.
>
> Signed-off-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx>
Assuming the PC compat code will be moved to
pc_*_2_5_machine_options(), because the patch will be included
after QEMU 2.5.0:
Reviewed-by: Eduardo Habkost <ehabkost@xxxxxxxxxx>
One comment below:
> ---
[...]
> diff --git a/target-i386/kvm.c b/target-i386/kvm.c
> index 1e811ee..2a0fd54 100644
> --- a/target-i386/kvm.c
> +++ b/target-i386/kvm.c
> @@ -2381,6 +2381,28 @@ int kvm_arch_put_registers(CPUState *cpu, int level)
> }
> }
>
> + if (level == KVM_PUT_FULL_STATE) {
> + /* kvm_arch_set_tsc_khz() below can be called in two control flows and
> + * we don't need to handle its errors in both of them.
> + *
> + * One is the control flow that creates a vcpu, where
> + * kvm_arch_set_tsc_khz() has already been called once before by
> + * kvm_arch_init_vcpu(). The latter will abort the control flow if there
> + * are any errors of kvm_arch_set_tsc_khz(). Thus, in this control flow,
> + * kvm_arch_set_tsc_khz() below never fails and we can safely ignore its
> + * return values here.
> + *
> + * Another is the control flow of migration that sets vcpu's TSC
> + * frequency on the destination. The only error that can fail the
> + * migration is the mismatch between the migrated and the user-specified
> + * TSC frequencies, which has been handled by cpu_post_load(). Other
> + * errors, i.e. those from kvm_arch_set_tsc_khz(), never fail the
> + * migration, so we also safely ignore its return values in this control
> + * flow.
> + */
This could be more succint. Something like:
/* We don't check for kvm_arch_set_tsc_khz() errors here, because
* TSC frequency mismatch shouldn't abort migration, unless the
* user explicitly asked for a more strict TSC setting (e.g.
* using an explicit "tsc-freq" option).
*/
No need to resubmit because of that, though. The comment can be
changed when applying the patch.
> + kvm_arch_set_tsc_khz(cpu);
> + }
> +
> ret = kvm_getput_regs(x86_cpu, 1);
> if (ret < 0) {
> return ret;
> diff --git a/target-i386/machine.c b/target-i386/machine.c
> index a18e16e..e560ca3 100644
> --- a/target-i386/machine.c
> +++ b/target-i386/machine.c
> @@ -6,6 +6,8 @@
> #include "cpu.h"
> #include "sysemu/kvm.h"
>
> +#include "qemu/error-report.h"
> +
> static const VMStateDescription vmstate_segment = {
> .name = "segment",
> .version_id = 1,
> @@ -331,6 +333,13 @@ static int cpu_post_load(void *opaque, int version_id)
> CPUX86State *env = &cpu->env;
> int i;
>
> + if (env->tsc_khz && env->user_tsc_khz &&
> + env->tsc_khz != env->user_tsc_khz) {
> + error_report("Mismatch between user-specified TSC frequency and "
> + "migrated TSC frequency");
> + return -EINVAL;
> + }
> +
> /*
> * Real mode guest segments register DPL should be zero.
> * Older KVM version were setting it wrongly.
> @@ -775,6 +784,26 @@ static const VMStateDescription vmstate_xss = {
> }
> };
>
> +static bool tsc_khz_needed(void *opaque)
> +{
> + X86CPU *cpu = opaque;
> + CPUX86State *env = &cpu->env;
> + MachineClass *mc = MACHINE_GET_CLASS(qdev_get_machine());
> + PCMachineClass *pcmc = PC_MACHINE_CLASS(mc);
> + return env->tsc_khz && pcmc->save_tsc_khz;
> +}
> +
> +static const VMStateDescription vmstate_tsc_khz = {
> + .name = "cpu/tsc_khz",
> + .version_id = 1,
> + .minimum_version_id = 1,
> + .needed = tsc_khz_needed,
> + .fields = (VMStateField[]) {
> + VMSTATE_INT64(env.tsc_khz, X86CPU),
> + VMSTATE_END_OF_LIST()
> + }
> +};
> +
> VMStateDescription vmstate_x86_cpu = {
> .name = "cpu",
> .version_id = 12,
> @@ -895,6 +924,7 @@ VMStateDescription vmstate_x86_cpu = {
> &vmstate_msr_hyperv_runtime,
> &vmstate_avx512,
> &vmstate_xss,
> + &vmstate_tsc_khz,
> NULL
> }
> };
> --
> 2.4.8
>
--
Eduardo
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