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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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6
arch/x86/kvm/x86.c
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@@ -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;