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>
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index ff4d406..d0e42f3 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -55,16 +55,16 @@
struct kvm_vcpu;
extern struct kmem_cache *kvm_vcpu_cache;
-/*
- * It would be nice to use something smarter than a linear search, TBD...
- * Thankfully we dont expect many devices to register (famous last words :),
- * so until then it will suffice. At least its abstracted so we can change
- * in one place.
- */
+struct kvm_io_range {
+ gpa_t addr;
+ int len;
+ struct kvm_io_device *dev;
+};
+
struct kvm_io_bus {
int dev_count;
#define NR_IOBUS_DEVS 300
- struct kvm_io_device *devs[NR_IOBUS_DEVS];
+ struct kvm_io_range range[NR_IOBUS_DEVS];
};
enum kvm_bus {
@@ -77,8 +77,8 @@
int len, const void *val);
int kvm_io_bus_read(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr, int len,
void *val);
-int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx,
- struct kvm_io_device *dev);
+int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
+ int len, struct kvm_io_device *dev);
int kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
struct kvm_io_device *dev);