Use the recently introduced call_srcu_expedited() when freeing the old I/O
bug during device registration to avoid triggering a non-expedited grace
period. Delaying the freeing of the object by a full grace period is a
complete non-issue, but the grace period also gets transferred to future
synchronizations, e.g. to the synchronize_srcu_expedited() invocation in
kvm_swap_active_memslots().
For micro-VM use cases, effectively transferring the non-expedited grace
period to memslot updates results in a meaningful delay in overall boot
time. E.g. with a CONFIG_HZ=100 kernel, the sync triggers a ~20ms delay,
increasing boot times by 15% or more.
Fixes: 7d9a0273c459 ("KVM: Avoid synchronize_srcu() in
kvm_io_bus_register_dev()")
Reported-by: Nikita Kalyazin <[email protected]>
Closes:
https://lore.kernel.org/all/[email protected]
Cc: Keir Fraser <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
---
virt/kvm/kvm_main.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 9faf70ccae7a..ceaf08a03428 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -6021,7 +6021,7 @@ int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus
bus_idx, gpa_t addr,
memcpy(new_bus->range + i + 1, bus->range + i,
(bus->dev_count - i) * sizeof(struct kvm_io_range));
rcu_assign_pointer(kvm->buses[bus_idx], new_bus);
- call_srcu(&kvm->srcu, &bus->rcu, __free_bus);
+ call_srcu_expedited(&kvm->srcu, &bus->rcu, __free_bus);
return 0;
}
--
2.53.0.473.g4a7958ca14-goog
