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:
----------
v4:
- replace loop with memset when setup empty irq routing table.
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 179df96b20f8..48b5d7fc108d 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -2068,6 +2068,7 @@ 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..266bab99a8a8 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;
+ int chip_size;
+
+ new = kzalloc(struct_size(new, map, 1), GFP_KERNEL_ACCOUNT);
+ if (!new)
+ return -ENOMEM;
+
+ new->nr_rt_entries = 1;
+
+ chip_size = sizeof(int) * KVM_NR_IRQCHIPS * KVM_IRQCHIP_NUM_PINS;
+ memset(new->chip, -1, chip_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 0f50960b0e3a..3438d6aa0f23 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1288,6 +1288,10 @@ 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]>
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 68f3f6c26046..6ee7ca39466e 100644
--- a/arch/x86/kvm/irq_comm.c
+++ b/arch/x86/kvm/irq_comm.c
@@ -397,11 +397,6 @@ 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 e02cc710f56d..eee3a0892137 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6469,9 +6469,6 @@ 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
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 ea63ac769889..78a1e2d801ba 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -2998,14 +2998,7 @@ 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