On Wed, Jul 20, 2011 at 03:11:58PM +0300, Sasha Levin wrote:
> 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.
>
> This should speed up all IO operations generated by the guest.
Some numbers, please.
> +int kvm_io_bus_find_closest_dev_idx(struct kvm_io_bus *bus,
> + gpa_t addr, int len)
> +{
> + int start = 0, end = bus->dev_count - 1;
> +
> + if (bus->dev_count == 0)
> + return -1;
> +
> + while (start <= end) {
> + int mid = (start + end) / 2;
> + struct kvm_io_range *range = &bus->range[mid];
> +
> + if (addr > range->addr)
> + start = mid + 1;
> + else if (addr < range->addr)
> + end = mid - 1;
If mid is zero, this assigns end = -1?
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