From mboxrd@z Thu Jan  1 00:00:00 1970
From: Marcelo Tosatti <mtosatti@redhat.com>
Subject: Re: [PATCH] IO: Intelligent device lookup on bus
Date: Wed, 20 Jul 2011 16:41:49 -0300
Message-ID: <20110720194149.GA21379@amt.cnet>
References: <1311163918-14334-1-git-send-email-levinsasha928@gmail.com>
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Cc: kvm@vger.kernel.org, Avi Kivity <avi@redhat.com>
To: Sasha Levin <levinsasha928@gmail.com>
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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?