linux-kernel - Re: [PATCH] kvm: remove in_range from kvm_io

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Date:	Tue, 23 Jun 2009 18:56:07 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Gregory Haskins <ghaskins@...ell.com>
Cc:	avi@...hat.com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	mtosatti@...hat.com, paulmck@...ux.vnet.ibm.com, markmc@...hat.com
Subject: Re: [PATCH] kvm: remove in_range from kvm_io_device

On Tue, Jun 23, 2009 at 11:44:57AM -0400, Gregory Haskins wrote:
> >>  This proposed approach forces us into a
> >> potential O(256) algorithm in the hotpath (all MMIO/PIO exits will hit
> >> this, not just in-kernel users).  How would you address this?
> >>     
> >
> > Two ideas that come to mind:
> > - add addr/len fields to devices, use these to speed up lookup
> >   
> 
> Yep, thats what I was thinking as well.  We can have the top-level
> (group) be an rbtree on addr/len, and then walk the list of items at
> that address linearly using your read/write() approach.
> 
> 
> > - add a small cache that can be scanned first
> >   
> 
> Yep, I think we may want to do this anyway independent of the search alg.
> 
> > In both cases, you first do a fast lookup, ask the device whether
> > it wants the transaction, then resort to linear scan if not
> >   
> 
> -Greg
> 

Looks like we have a concensus then.

-- 
MST
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