11:37 a.m.
On Mon, Sep 28, 2015 at 01:38:31PM +0800, Haozhong Zhang wrote:
When a vcpu is created in KVM, its TSC rate is initially identical
to
the host TSC rate. If its state is migrated to a vcpu on another
machine (target machine) which may uses a different host TSC rate, QEMU
on the target machine should notice KVM of the migrated vcpu's TSC
rate. In case that KVM on the target machine supports TSC scaling, guest
programs running on the migrated vcpu will observe the same TSC rate
before and after the migration.
Signed-off-by: Haozhong Zhang <haozhong.zhang(a)intel.com>
---
kvm-all.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/kvm-all.c b/kvm-all.c
index 0be4615..e8de038 100644
--- a/kvm-all.c
+++ b/kvm-all.c
@@ -1769,6 +1769,19 @@ void kvm_cpu_synchronize_post_reset(CPUState *cpu)
static void do_kvm_cpu_synchronize_post_init(void *arg)
{
CPUState *cpu = arg;
+ CPUX86State *env = &X86_CPU(cpu)->env;
+ int r;
+
+ /*
+ * XXX: KVM_SET_TSC_KHZ must be done before kvm_arch_put_registers().
Could you explain where this requirement comes from?
+ */
+ r = kvm_check_extension(cpu->kvm_state, KVM_CAP_TSC_CONTROL);
+ if (r && env->tsc_khz) {
+ r = kvm_vcpu_ioctl(cpu, KVM_SET_TSC_KHZ, env->tsc_khz);
+ if (r < 0) {
+ fprintf(stderr, "KVM_SET_TSC_KHZ failed\n");
+ }
+ }
This is duplicating the existing KVM_SET_TSC_KHZ call at
kvm_arch_init_vcpu(). I wonder if there's a way to avoid this
duplication. Should we set TSC KHz only at
do_kvm_cpu_synchronize_post_init(), and remove the call from
kvm_arch_init_vcpu()?
Or maybe we shouldn't treat this as VM state, but as configuration, and
let management configure the TSC frequency explicitly if the user really
needs it to stay the same during migration.
(CCing libvir-list to see if they have feedback)
--
Eduardo
10:43 p.m.
New subject: [libvirt] [PATCH 3/3] kvm-all: notice KVM of vcpu's TSC rate after migration
On Mon, Sep 28, 2015 at 01:37:34PM -0300, Eduardo Habkost wrote:
On Mon, Sep 28, 2015 at 01:38:31PM +0800, Haozhong Zhang wrote:
> When a vcpu is created in KVM, its TSC rate is initially identical to
> the host TSC rate. If its state is migrated to a vcpu on another
> machine (target machine) which may uses a different host TSC rate, QEMU
> on the target machine should notice KVM of the migrated vcpu's TSC
> rate. In case that KVM on the target machine supports TSC scaling, guest
> programs running on the migrated vcpu will observe the same TSC rate
> before and after the migration.
>
> Signed-off-by: Haozhong Zhang <haozhong.zhang(a)intel.com>
> ---
> kvm-all.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/kvm-all.c b/kvm-all.c
> index 0be4615..e8de038 100644
> --- a/kvm-all.c
> +++ b/kvm-all.c
> @@ -1769,6 +1769,19 @@ void kvm_cpu_synchronize_post_reset(CPUState *cpu)
> static void do_kvm_cpu_synchronize_post_init(void *arg)
> {
> CPUState *cpu = arg;
> + CPUX86State *env = &X86_CPU(cpu)->env;
> + int r;
> +
> + /*
> + * XXX: KVM_SET_TSC_KHZ must be done before kvm_arch_put_registers().
Could you explain where this requirement comes from?
kvm_arch_put_registers() below will setup vcpu's MSR_IA32_TSC through
KVM ioctl KVM_SET_MSRS. KVM needs to know vcpu's TSC rate so as to
correctly scale the TSC value given by QEMU, especially when vcpu's
TSC rate is different than the host TSC rate (e.g. it's migrated from
another machine w/ different host TSC rate than the current one).
> + */
> + r = kvm_check_extension(cpu->kvm_state, KVM_CAP_TSC_CONTROL);
> + if (r && env->tsc_khz) {
> + r = kvm_vcpu_ioctl(cpu, KVM_SET_TSC_KHZ, env->tsc_khz);
> + if (r < 0) {
> + fprintf(stderr, "KVM_SET_TSC_KHZ failed\n");
> + }
> + }
This is duplicating the existing KVM_SET_TSC_KHZ call at
kvm_arch_init_vcpu(). I wonder if there's a way to avoid this
duplication. Should we set TSC KHz only at
do_kvm_cpu_synchronize_post_init(), and remove the call from
kvm_arch_init_vcpu()?
I'll check if it's safe to remove the call from kvm_arch_init_vcpu().
Or maybe we shouldn't treat this as VM state, but as
configuration, and
let management configure the TSC frequency explicitly if the user really
needs it to stay the same during migration.
(CCing libvir-list to see if they have feedback)
Thanks for CC. I'll consider to add a command line option to control
the configuration of guest TSC fequency.
--
Eduardo
1:02 p.m.
New subject: [libvirt] [PATCH 3/3] kvm-all: notice KVM of vcpu's TSC rate after migration
On Tue, Sep 29, 2015 at 11:43:34AM +0800, Haozhong Zhang wrote:
[...]
> > Or maybe we shouldn't treat this as VM state, but as configuration, and
> > let management configure the TSC frequency explicitly if the user really
> > needs it to stay the same during migration.
> >
> > (CCing libvir-list to see if they have feedback)
> >
> Thanks for CC. I'll consider to add a command line
option to control
> the configuration of guest TSC fequency.
It already exists, -cpu has a "tsc-freq" option.
--
Eduardo
On Mon, Sep 28, 2015 at 01:37:34PM -0300, Eduardo Habkost wrote:
> On Mon, Sep 28, 2015 at 01:38:31PM +0800, Haozhong Zhang wrote:
[...]
> > static void do_kvm_cpu_synchronize_post_init(void *arg)
> > {
> > CPUState *cpu = arg;
> > + CPUX86State *env = &X86_CPU(cpu)->env;
> > + int r;
> > +
> > + /*
> > + * XXX: KVM_SET_TSC_KHZ must be done before kvm_arch_put_registers().
> Could you explain where this requirement comes from?
>
kvm_arch_put_registers() below will setup vcpu's MSR_IA32_TSC through
KVM ioctl KVM_SET_MSRS. KVM needs to know vcpu's TSC rate so as to
correctly scale the TSC value given by QEMU, especially when vcpu's
TSC rate is different than the host TSC rate (e.g. it's migrated from
another machine w/ different host TSC rate than the current one).
Thanks. The comment above could contain a short version of this
explanation, e.g.: "KVM needs KVM_SET_TSC_KHZ to be done before
KVM_SET_MSRS sets MSR_IA32_TSC (done by kvm_arch_put_registers())".
7:32 p.m.
New subject: [libvirt] [PATCH 3/3] kvm-all: notice KVM of vcpu's TSC rate after migration
On Tue, Sep 29, 2015 at 03:02:07PM -0300, Eduardo Habkost wrote:
On Tue, Sep 29, 2015 at 11:43:34AM +0800, Haozhong Zhang wrote:
> On Mon, Sep 28, 2015 at 01:37:34PM -0300, Eduardo Habkost wrote:
> > On Mon, Sep 28, 2015 at 01:38:31PM +0800, Haozhong Zhang wrote:
[...]
> > > static void do_kvm_cpu_synchronize_post_init(void *arg)
> > > {
> > > CPUState *cpu = arg;
> > > + CPUX86State *env = &X86_CPU(cpu)->env;
> > > + int r;
> > > +
> > > + /*
> > > + * XXX: KVM_SET_TSC_KHZ must be done before
kvm_arch_put_registers().
> >
> > Could you explain where this requirement comes from?
> >
>
> kvm_arch_put_registers() below will setup vcpu's MSR_IA32_TSC through
> KVM ioctl KVM_SET_MSRS. KVM needs to know vcpu's TSC rate so as to
> correctly scale the TSC value given by QEMU, especially when vcpu's
> TSC rate is different than the host TSC rate (e.g. it's migrated from
> another machine w/ different host TSC rate than the current one).
Thanks. The comment above could contain a short version of this
explanation, e.g.: "KVM needs KVM_SET_TSC_KHZ to be done before
KVM_SET_MSRS sets MSR_IA32_TSC (done by kvm_arch_put_registers())".
will include this in the comment
>
[...]
> > Or maybe we shouldn't treat this as VM state, but as configuration, and
> > let management configure the TSC frequency explicitly if the user really
> > needs it to stay the same during migration.
> >
> > (CCing libvir-list to see if they have feedback)
> >
>
> Thanks for CC. I'll consider to add a command line option to control
> the configuration of guest TSC fequency.
It already exists, -cpu has a "tsc-freq" option.
What I'm considering is to add a "-keep-tsc-freq" option to control
whether the TSC frequency should be migrated if "tsc-freq" is not
presented. Compared to "tsc-freq", "-keep-tsc-freq" can free users
from figuring out the guest TSC frequency manually in the migration.
- Haozhong
--
Eduardo
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3:36 p.m.
New subject: [libvirt] [PATCH 3/3] kvm-all: notice KVM of vcpu's TSC rate after migration
On Wed, Sep 30, 2015 at 08:32:26AM +0800, Haozhong Zhang wrote:
> [...]
> > > Or maybe we shouldn't treat this as VM state, but as configuration,
and
> > > let management configure the TSC frequency explicitly if the user really
> > > needs it to stay the same during migration.
> > >
> > > (CCing libvir-list to see if they have feedback)
> > >
> >
> > Thanks for CC. I'll consider to add a command line option to control
> > the configuration of guest TSC fequency.
>
> It already exists, -cpu has a "tsc-freq" option.
>
What I'm considering is to add a "-keep-tsc-freq" option to control
whether the TSC frequency should be migrated if "tsc-freq" is not
presented. Compared to "tsc-freq", "-keep-tsc-freq" can free users
from figuring out the guest TSC frequency manually in the migration.
If you do that, please make it a property of the CPU object, so it will
can be set as a "-cpu" option.
--
Eduardo
8:20 p.m.
New subject: [libvirt] [PATCH 3/3] kvm-all: notice KVM of vcpu's TSC rate after migration
On Wed, Sep 30, 2015 at 05:36:11PM -0300, Eduardo Habkost wrote:
On Wed, Sep 30, 2015 at 08:32:26AM +0800, Haozhong Zhang wrote:
> > [...]
> > > > Or maybe we shouldn't treat this as VM state, but as
configuration, and
> > > > let management configure the TSC frequency explicitly if the user
really
> > > > needs it to stay the same during migration.
> > > >
> > > > (CCing libvir-list to see if they have feedback)
> > > >
> > >
> > > Thanks for CC. I'll consider to add a command line option to control
> > > the configuration of guest TSC fequency.
> >
> > It already exists, -cpu has a "tsc-freq" option.
> >
>
> What I'm considering is to add a "-keep-tsc-freq" option to control
> whether the TSC frequency should be migrated if "tsc-freq" is not
> presented. Compared to "tsc-freq", "-keep-tsc-freq" can free
users
> from figuring out the guest TSC frequency manually in the migration.
If you do that, please make it a property of the CPU object, so it will
can be set as a "-cpu" option.
Yes, I'll do so.
- Haozhong
--
Eduardo
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