KVM: Intelligent device lookup on I/O bus

Currently the method of dealing with an IO operation on a bus (PIO/MMIO)
is to call the read or write callback for each device registered
on the bus until we find a device which handles it.

Since the number of devices on a bus can be significant due to ioeventfds
and coalesced MMIO zones, this leads to a lot of overhead on each IO
operation.

Instead of registering devices, we now register ranges which points to
a device. Lookup is done using an efficient bsearch instead of a linear
search.

Performance test was conducted by comparing exit count per second with
200 ioeventfds created on one byte and the guest is trying to access a
different byte continuously (triggering usermode exits).
Before the patch the guest has achieved 259k exits per second, after the
patch the guest does 274k exits per second.

Cc: Avi Kivity <avi@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6cb353c83a12..d28dff749dfd 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3562,7 +3562,11 @@ long kvm_arch_vm_ioctl(struct file *filp,
                         if (r) {
                                 mutex_lock(&kvm->slots_lock);
                                 kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS,
-                                                          &vpic->dev);
+                                                          &vpic->dev_master);
+                                kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS,
+                                                          &vpic->dev_slave);
+                                kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS,
+                                                          &vpic->dev_eclr);
                                 mutex_unlock(&kvm->slots_lock);
                                 kfree(vpic);
                                 goto create_irqchip_unlock;