From: Yi Wang <[email protected]>
We found that it may cost more than 20 milliseconds very accidentally
to enable cap of KVM_CAP_SPLIT_IRQCHIP on a host which has many vms
already.
The reason is that when vmm(qemu/CloudHypervisor) invokes
KVM_CAP_SPLIT_IRQCHIP kvm will call synchronize_srcu_expedited() and
might_sleep and kworker of srcu may cost some delay during this period.
One way makes sence is setup empty irq routing when creating vm and
so that x86/s390 don't need to setup empty/dummy irq routing.
Note: I have no s390 machine so this patch has not been tested
thoroughly on s390 platform. Thanks to Christian for a quick test on
s390 and it still seems to work[1].
Changelog:
----------
v3:
- squash setup empty routing function and use of that into one commit
- drop the comment in s390 part
v2:
- setup empty irq routing in kvm_create_vm
- don't setup irq routing in x86 KVM_CAP_SPLIT_IRQCHIP
- don't setup irq routing in s390 KVM_CREATE_IRQCHIP
v1: https://lore.kernel.org/kvm/[email protected]/
1. https://lore.kernel.org/lkml/[email protected]/
Yi Wang (3):
KVM: setup empty irq routing when create vm
KVM: x86: don't setup empty irq routing when KVM_CAP_SPLIT_IRQCHIP
KVM: s390: don't setup dummy routing when KVM_CREATE_IRQCHIP
arch/s390/kvm/kvm-s390.c | 9 +--------
arch/x86/kvm/irq.h | 1 -
arch/x86/kvm/irq_comm.c | 5 -----
arch/x86/kvm/x86.c | 3 ---
include/linux/kvm_host.h | 1 +
virt/kvm/irqchip.c | 19 +++++++++++++++++++
virt/kvm/kvm_main.c | 4 ++++
7 files changed, 25 insertions(+), 17 deletions(-)
--
2.39.3
From: Yi Wang <[email protected]>
Add a new function to setup empty irq routing in kvm path, which
can be invoded in non-architecture-specific functions. The difference
compared to the kvm_setup_empty_irq_routing() is this function just
alloc the empty irq routing and does not need synchronize srcu, as
we will call it in kvm_create_vm().
Using the new adding function, we can setup empty irq routing when
kvm_create_vm(), so that x86 and s390 no longer need to set
empty/dummy irq routing when creating an IRQCHIP 'cause it avoid
an synchronize_srcu.
Signed-off-by: Yi Wang <[email protected]>
---
include/linux/kvm_host.h | 1 +
virt/kvm/irqchip.c | 19 +++++++++++++++++++
virt/kvm/kvm_main.c | 4 ++++
3 files changed, 24 insertions(+)
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 4944136efaa2..e91525c0a4ea 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -2000,6 +2000,7 @@ int kvm_set_irq_routing(struct kvm *kvm,
const struct kvm_irq_routing_entry *entries,
unsigned nr,
unsigned flags);
+int kvm_setup_empty_irq_routing_lockless(struct kvm *kvm);
int kvm_set_routing_entry(struct kvm *kvm,
struct kvm_kernel_irq_routing_entry *e,
const struct kvm_irq_routing_entry *ue);
diff --git a/virt/kvm/irqchip.c b/virt/kvm/irqchip.c
index 1e567d1f6d3d..90fc43bd0fe4 100644
--- a/virt/kvm/irqchip.c
+++ b/virt/kvm/irqchip.c
@@ -237,3 +237,22 @@ int kvm_set_irq_routing(struct kvm *kvm,
return r;
}
+
+int kvm_setup_empty_irq_routing_lockless(struct kvm *kvm)
+{
+ struct kvm_irq_routing_table *new;
+ u32 i, j;
+
+ new = kzalloc(struct_size(new, map, 1), GFP_KERNEL_ACCOUNT);
+ if (!new)
+ return -ENOMEM;
+
+ new->nr_rt_entries = 1;
+ for (i = 0; i < KVM_NR_IRQCHIPS; i++)
+ for (j = 0; j < KVM_IRQCHIP_NUM_PINS; j++)
+ new->chip[i][j] = -1;
+
+ RCU_INIT_POINTER(kvm->irq_routing, new);
+
+ return 0;
+}
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 7db96875ac46..db1b13fc0502 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1242,6 +1242,10 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
if (r)
goto out_err;
+ r = kvm_setup_empty_irq_routing_lockless(kvm);
+ if (r)
+ goto out_err;
+
mutex_lock(&kvm_lock);
list_add(&kvm->vm_list, &vm_list);
mutex_unlock(&kvm_lock);
--
2.39.3
From: Yi Wang <[email protected]>
As we have setup empty irq routing in kvm_create_vm(), there's
no need to setup dummy routing when KVM_CREATE_IRQCHIP.
Signed-off-by: Yi Wang <[email protected]>
---
arch/s390/kvm/kvm-s390.c | 9 +--------
1 file changed, 1 insertion(+), 8 deletions(-)
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index acc81ca6492e..dec3c026a6c1 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -2999,14 +2999,7 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
break;
}
case KVM_CREATE_IRQCHIP: {
- struct kvm_irq_routing_entry routing;
-
- r = -EINVAL;
- if (kvm->arch.use_irqchip) {
- /* Set up dummy routing. */
- memset(&routing, 0, sizeof(routing));
- r = kvm_set_irq_routing(kvm, &routing, 0, 0);
- }
+ r = 0;
break;
}
case KVM_SET_DEVICE_ATTR: {
--
2.39.3
On 2/28/24 22:53, Yi Wang wrote:
> From: Yi Wang <[email protected]>
>
> Add a new function to setup empty irq routing in kvm path, which
> can be invoded in non-architecture-specific functions. The difference
:s/invoded/invoked/
Dongli Zhang
From: Yi Wang <[email protected]>
We found that it may cost more than 20 milliseconds very accidentally
to enable cap of KVM_CAP_SPLIT_IRQCHIP on a host which has many vms
already.
The reason is that when vmm(qemu/CloudHypervisor) invokes
KVM_CAP_SPLIT_IRQCHIP kvm will call synchronize_srcu_expedited() and
might_sleep and kworker of srcu may cost some delay during this period.
As we have set up empty irq routing when creating vm, so this is no
need now.
Signed-off-by: Yi Wang <[email protected]>
---
arch/x86/kvm/irq.h | 1 -
arch/x86/kvm/irq_comm.c | 5 -----
arch/x86/kvm/x86.c | 3 ---
3 files changed, 9 deletions(-)
diff --git a/arch/x86/kvm/irq.h b/arch/x86/kvm/irq.h
index c2d7cfe82d00..76d46b2f41dd 100644
--- a/arch/x86/kvm/irq.h
+++ b/arch/x86/kvm/irq.h
@@ -106,7 +106,6 @@ void __kvm_migrate_timers(struct kvm_vcpu *vcpu);
int apic_has_pending_timer(struct kvm_vcpu *vcpu);
int kvm_setup_default_irq_routing(struct kvm *kvm);
-int kvm_setup_empty_irq_routing(struct kvm *kvm);
int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
struct kvm_lapic_irq *irq,
struct dest_map *dest_map);
diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
index 16d076a1b91a..99bf53b94175 100644
--- a/arch/x86/kvm/irq_comm.c
+++ b/arch/x86/kvm/irq_comm.c
@@ -392,11 +392,6 @@ int kvm_setup_default_irq_routing(struct kvm *kvm)
static const struct kvm_irq_routing_entry empty_routing[] = {};
-int kvm_setup_empty_irq_routing(struct kvm *kvm)
-{
- return kvm_set_irq_routing(kvm, empty_routing, 0, 0);
-}
-
void kvm_arch_post_irq_routing_update(struct kvm *kvm)
{
if (!irqchip_split(kvm))
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index cec0fc2a4b1c..6a2e786aca22 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6414,9 +6414,6 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
goto split_irqchip_unlock;
if (kvm->created_vcpus)
goto split_irqchip_unlock;
- r = kvm_setup_empty_irq_routing(kvm);
- if (r)
- goto split_irqchip_unlock;
/* Pairs with irqchip_in_kernel. */
smp_wmb();
kvm->arch.irqchip_mode = KVM_IRQCHIP_SPLIT;
--
2.39.3
On Thu, Feb 29, 2024 at 6:15 PM Dongli Zhang <[email protected]> wrote:
>
>
>
> On 2/28/24 22:53, Yi Wang wrote:
> > From: Yi Wang <[email protected]>
> >
> > Add a new function to setup empty irq routing in kvm path, which
> > can be invoded in non-architecture-specific functions. The difference
>
> :s/invoded/invoked/
Thanks for pointing this out.
Sean, Oliver, Christian, Do you have any other thoughts? Any
suggestions are appreciated.
>
> Dongli Zhang
--
---
Best wishes
Yi Wang
On 2/29/2024 2:53 PM, Yi Wang wrote:
> From: Yi Wang <[email protected]>
>
> Add a new function to setup empty irq routing in kvm path, which
> can be invoded in non-architecture-specific functions. The difference
> compared to the kvm_setup_empty_irq_routing() is this function just
> alloc the empty irq routing and does not need synchronize srcu, as
> we will call it in kvm_create_vm().
>
> Using the new adding function, we can setup empty irq routing when
> kvm_create_vm(), so that x86 and s390 no longer need to set
> empty/dummy irq routing when creating an IRQCHIP 'cause it avoid
> an synchronize_srcu.
>
> Signed-off-by: Yi Wang <[email protected]>
> ---
> include/linux/kvm_host.h | 1 +
> virt/kvm/irqchip.c | 19 +++++++++++++++++++
> virt/kvm/kvm_main.c | 4 ++++
> 3 files changed, 24 insertions(+)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 4944136efaa2..e91525c0a4ea 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -2000,6 +2000,7 @@ int kvm_set_irq_routing(struct kvm *kvm,
> const struct kvm_irq_routing_entry *entries,
> unsigned nr,
> unsigned flags);
> +int kvm_setup_empty_irq_routing_lockless(struct kvm *kvm);
> int kvm_set_routing_entry(struct kvm *kvm,
> struct kvm_kernel_irq_routing_entry *e,
> const struct kvm_irq_routing_entry *ue);
> diff --git a/virt/kvm/irqchip.c b/virt/kvm/irqchip.c
> index 1e567d1f6d3d..90fc43bd0fe4 100644
> --- a/virt/kvm/irqchip.c
> +++ b/virt/kvm/irqchip.c
> @@ -237,3 +237,22 @@ int kvm_set_irq_routing(struct kvm *kvm,
>
> return r;
> }
> +
> +int kvm_setup_empty_irq_routing_lockless(struct kvm *kvm)
> +{
> + struct kvm_irq_routing_table *new;
> + u32 i, j;
> +
> + new = kzalloc(struct_size(new, map, 1), GFP_KERNEL_ACCOUNT);
> + if (!new)
> + return -ENOMEM;
> +
> + new->nr_rt_entries = 1;
> + for (i = 0; i < KVM_NR_IRQCHIPS; i++)
> + for (j = 0; j < KVM_IRQCHIP_NUM_PINS; j++)
> + new->chip[i][j] = -1;
Maybe it looks nicer by:
size = sizeof(int) * KVM_NR_IRQCHIPS *KVM_IRQCHIP_NUM_PINS;
memset(new->chip, -1, size);
> +
> + RCU_INIT_POINTER(kvm->irq_routing, new);
> +
> + return 0;
> +}
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 7db96875ac46..db1b13fc0502 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1242,6 +1242,10 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
> if (r)
> goto out_err;
>
> + r = kvm_setup_empty_irq_routing_lockless(kvm);
> + if (r)
> + goto out_err;
> +
> mutex_lock(&kvm_lock);
> list_add(&kvm->vm_list, &vm_list);
> mutex_unlock(&kvm_lock);
On Fri, Mar 8, 2024 at 12:06 PM Yang, Weijiang <weijiang.yang@intelcom> wrote:
>
> On 2/29/2024 2:53 PM, Yi Wang wrote:
> > From: Yi Wang <[email protected]>
> > +
> > +int kvm_setup_empty_irq_routing_lockless(struct kvm *kvm)
> > +{
> > + struct kvm_irq_routing_table *new;
> > + u32 i, j;
> > +
> > + new = kzalloc(struct_size(new, map, 1), GFP_KERNEL_ACCOUNT);
> > + if (!new)
> > + return -ENOMEM;
> > +
> > + new->nr_rt_entries = 1;
> > + for (i = 0; i < KVM_NR_IRQCHIPS; i++)
> > + for (j = 0; j < KVM_IRQCHIP_NUM_PINS; j++)
> > + new->chip[i][j] = -1;
>
> Maybe it looks nicer by:
> size = sizeof(int) * KVM_NR_IRQCHIPS *KVM_IRQCHIP_NUM_PINS;
> memset(new->chip, -1, size);
>
It seems better, I'll update this patch. Thx a lot!
> > +
> > + RCU_INIT_POINTER(kvm->irq_routing, new);
> > +
> > + return 0;
>
---
Best wishes
Yi Wang