From: Wanpeng Li <[email protected]>
Commit 61abdbe0bcc2 ("kvm: x86: make lapic hrtimer pinned") pinned the
lapic timer to avoid to wait until the next kvm exit for the guest to
see KVM_REQ_PENDING_TIMER set. There is another solution to give a kick
after setting the KVM_REQ_PENDING_TIMER bit, make lapic timer unpinned
will be used in follow up patches.
Cc: Paolo Bonzini <[email protected]>
Cc: Radim Krčmář <[email protected]>
Cc: Marcelo Tosatti <[email protected]>
Signed-off-by: Wanpeng Li <[email protected]>
---
arch/x86/kvm/lapic.c | 8 ++++----
arch/x86/kvm/x86.c | 6 +-----
2 files changed, 5 insertions(+), 9 deletions(-)
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 459d1ee..707ca9c 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1582,7 +1582,7 @@ static void start_sw_tscdeadline(struct kvm_lapic *apic)
likely(ns > apic->lapic_timer.timer_advance_ns)) {
expire = ktime_add_ns(now, ns);
expire = ktime_sub_ns(expire, ktimer->timer_advance_ns);
- hrtimer_start(&ktimer->timer, expire, HRTIMER_MODE_ABS_PINNED);
+ hrtimer_start(&ktimer->timer, expire, HRTIMER_MODE_ABS);
} else
apic_timer_expired(apic);
@@ -1684,7 +1684,7 @@ static void start_sw_period(struct kvm_lapic *apic)
hrtimer_start(&apic->lapic_timer.timer,
apic->lapic_timer.target_expiration,
- HRTIMER_MODE_ABS_PINNED);
+ HRTIMER_MODE_ABS);
}
bool kvm_lapic_hv_timer_in_use(struct kvm_vcpu *vcpu)
@@ -2321,7 +2321,7 @@ int kvm_create_lapic(struct kvm_vcpu *vcpu, int timer_advance_ns)
apic->vcpu = vcpu;
hrtimer_init(&apic->lapic_timer.timer, CLOCK_MONOTONIC,
- HRTIMER_MODE_ABS_PINNED);
+ HRTIMER_MODE_ABS);
apic->lapic_timer.timer.function = apic_timer_fn;
if (timer_advance_ns == -1) {
apic->lapic_timer.timer_advance_ns = LAPIC_TIMER_ADVANCE_ADJUST_INIT;
@@ -2510,7 +2510,7 @@ void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)
timer = &vcpu->arch.apic->lapic_timer.timer;
if (hrtimer_cancel(timer))
- hrtimer_start_expires(timer, HRTIMER_MODE_ABS_PINNED);
+ hrtimer_start_expires(timer, HRTIMER_MODE_ABS);
}
/*
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3a7cd935..e199ac7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1437,12 +1437,8 @@ static void update_pvclock_gtod(struct timekeeper *tk)
void kvm_set_pending_timer(struct kvm_vcpu *vcpu)
{
- /*
- * Note: KVM_REQ_PENDING_TIMER is implicitly checked in
- * vcpu_enter_guest. This function is only called from
- * the physical CPU that is running vcpu.
- */
kvm_make_request(KVM_REQ_PENDING_TIMER, vcpu);
+ kvm_vcpu_kick(vcpu);
}
static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
--
1.8.3.1
On Sat, 2019-07-06 at 09:26 +0800, Wanpeng Li wrote:
> From: Wanpeng Li <[email protected]>
>
> Commit 61abdbe0bcc2 ("kvm: x86: make lapic hrtimer pinned") pinned the
> lapic timer to avoid to wait until the next kvm exit for the guest to
> see KVM_REQ_PENDING_TIMER set. There is another solution to give a kick
> after setting the KVM_REQ_PENDING_TIMER bit, make lapic timer unpinned
> will be used in follow up patches.
>
> Cc: Paolo Bonzini <[email protected]>
> Cc: Radim Krčmář <[email protected]>
> Cc: Marcelo Tosatti <[email protected]>
> Signed-off-by: Wanpeng Li <[email protected]>
> ---
> arch/x86/kvm/lapic.c | 8 ++++----
> arch/x86/kvm/x86.c | 6 +-----
> 2 files changed, 5 insertions(+), 9 deletions(-)
...
> @@ -2510,7 +2510,7 @@ void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)
>
> timer = &vcpu->arch.apic->lapic_timer.timer;
> if (hrtimer_cancel(timer))
> - hrtimer_start_expires(timer, HRTIMER_MODE_ABS_PINNED);
> + hrtimer_start_expires(timer, HRTIMER_MODE_ABS);
> }
>
> /*
Wait, in that case why are we even bothering to cancel and restart the
timer? I thought the whole point of that was to pin it to the *new* CPU
that this vCPU is running on.
If not, can't we just kill __kvm_migrate_apic_timer() off completely
not?
On Wed, 2022-03-09 at 08:24 -0300, Marcelo Tosatti wrote:
> On Wed, Mar 09, 2022 at 10:26:51AM +0100, David Woodhouse wrote:
> > On Sat, 2019-07-06 at 09:26 +0800, Wanpeng Li wrote:
> > > From: Wanpeng Li <[email protected]>
> > >
> > > Commit 61abdbe0bcc2 ("kvm: x86: make lapic hrtimer pinned") pinned the
> > > lapic timer to avoid to wait until the next kvm exit for the guest to
> > > see KVM_REQ_PENDING_TIMER set. There is another solution to give a kick
> > > after setting the KVM_REQ_PENDING_TIMER bit, make lapic timer unpinned
> > > will be used in follow up patches.
> > >
> > > Cc: Paolo Bonzini <[email protected]>
> > > Cc: Radim Krčmář <[email protected]>
> > > Cc: Marcelo Tosatti <[email protected]>
> > > Signed-off-by: Wanpeng Li <[email protected]>
> > > ---
> > > arch/x86/kvm/lapic.c | 8 ++++----
> > > arch/x86/kvm/x86.c | 6 +-----
> > > 2 files changed, 5 insertions(+), 9 deletions(-)
> >
> > ...
> >
> >
> > > @@ -2510,7 +2510,7 @@ void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)
> > >
> > > timer = &vcpu->arch.apic->lapic_timer.timer;
> > > if (hrtimer_cancel(timer))
> > > - hrtimer_start_expires(timer, HRTIMER_MODE_ABS_PINNED);
> > > + hrtimer_start_expires(timer, HRTIMER_MODE_ABS);
> > > }
> > >
> > > /*
> >
> > Wait, in that case why are we even bothering to cancel and restart the
> > timer? I thought the whole point of that was to pin it to the *new* CPU
> > that this vCPU is running on.
> >
> > If not, can't we just kill __kvm_migrate_apic_timer() off completely
> > not?
>
> Current code looks like this:
>
> void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)
> {
> struct hrtimer *timer;
>
> if (!lapic_in_kernel(vcpu) ||
> kvm_can_post_timer_interrupt(vcpu)) <----------
> return;
>
> timer = &vcpu->arch.apic->lapic_timer.timer;
> if (hrtimer_cancel(timer))
> hrtimer_start_expires(timer, HRTIMER_MODE_ABS_HARD);
> }
>
> Yeah, should be HRTIMER_MODE_ABS_PINNED AFAICS.
No, it's *intentionally* not pinned any more, since this patch that I'm
replying to, which became commit 4d151bf3b89. It doesn't *have* to run
on the same physical CPU, because of the epiphany that it can just call
kvm_vcpu_kick() after making the request.
But if it's a recurring timer it's still *best* for it to run on the
same physical CPU, just for cache locality reasons. So I think I was
wrong; the migration *isn't* pointless. It's still a valid
optimisation; it's just not *mandatory* any more.
On Wed, Mar 09, 2022 at 10:26:51AM +0100, David Woodhouse wrote:
> On Sat, 2019-07-06 at 09:26 +0800, Wanpeng Li wrote:
> > From: Wanpeng Li <[email protected]>
> >
> > Commit 61abdbe0bcc2 ("kvm: x86: make lapic hrtimer pinned") pinned the
> > lapic timer to avoid to wait until the next kvm exit for the guest to
> > see KVM_REQ_PENDING_TIMER set. There is another solution to give a kick
> > after setting the KVM_REQ_PENDING_TIMER bit, make lapic timer unpinned
> > will be used in follow up patches.
> >
> > Cc: Paolo Bonzini <[email protected]>
> > Cc: Radim Krčmář <[email protected]>
> > Cc: Marcelo Tosatti <[email protected]>
> > Signed-off-by: Wanpeng Li <[email protected]>
> > ---
> > arch/x86/kvm/lapic.c | 8 ++++----
> > arch/x86/kvm/x86.c | 6 +-----
> > 2 files changed, 5 insertions(+), 9 deletions(-)
>
> ...
>
>
> > @@ -2510,7 +2510,7 @@ void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)
> >
> > timer = &vcpu->arch.apic->lapic_timer.timer;
> > if (hrtimer_cancel(timer))
> > - hrtimer_start_expires(timer, HRTIMER_MODE_ABS_PINNED);
> > + hrtimer_start_expires(timer, HRTIMER_MODE_ABS);
> > }
> >
> > /*
>
> Wait, in that case why are we even bothering to cancel and restart the
> timer? I thought the whole point of that was to pin it to the *new* CPU
> that this vCPU is running on.
>
> If not, can't we just kill __kvm_migrate_apic_timer() off completely
> not?
Current code looks like this:
void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)
{
struct hrtimer *timer;
if (!lapic_in_kernel(vcpu) ||
kvm_can_post_timer_interrupt(vcpu)) <----------
return;
timer = &vcpu->arch.apic->lapic_timer.timer;
if (hrtimer_cancel(timer))
hrtimer_start_expires(timer, HRTIMER_MODE_ABS_HARD);
}
Yeah, should be HRTIMER_MODE_ABS_PINNED AFAICS.