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KVM: Intelligent device lookup on I/O bus

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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>
This commit is contained in:
Sasha Levin
2011-07-27 16:00:48 +03:00
committed by Avi Kivity
parent 0d460ffc09
commit 743eeb0b01
9 changed files with 216 additions and 47 deletions
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18
include/linux/kvm_host.h
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@@ -55,16 +55,16 @@ struct kvm;
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 kvm_io_bus_write(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
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);