Re: [PATCH v4] IO: Intelligent device lookup on bus

[Avi Kivity <avi@redhat.com>]

On 07/27/2011 04:00 PM, 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.
>
> 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.
>

Applied, thanks.

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