linux-kernel - Re: [PATCH v10 2/2] kvm: Add resampling irqfds for level triggered interrupts

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Message-ID: <1348062872.28860.24.camel@bling.home>
Date:	Wed, 19 Sep 2012 07:54:32 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>, gleb@...hat.com,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 2/2] kvm: Add resampling irqfds for level triggered
 interrupts

On Wed, 2012-09-19 at 12:10 +0300, Avi Kivity wrote:
> On 09/19/2012 12:08 PM, Michael S. Tsirkin wrote:
> 
> >> Whoa.  Can't we put the resampler entry somewhere we don't need to
> >> search for it?  Like a kvm_kernel_irq_routing_entry, that's indexed by
> >> gsi already (kvm_irq_routing_table::rt_entries[gsi]).
> > 
> > I'm not sure why would we bother optimizing this,
> 
> Not optimizing, simplifying.
> 
> > but if we do, I guess we could look for the irq notifier
> > which is already indexed by gsi.
> 
> It's not, it's looked up in a list.


I'm not sure it's a simplification because to index by gsi we suddenly
need to care how many gsis there are.  I believe that currently means we
have to assume an ioapic.  Creating a dumb list is a little bit of
overhead, but we get to stay blissfully unaware of the gsi
implementation.  Practically we're looking at a list of 4 entries, maybe
a few times that when we expose more PCI root bridges to the guest.
Thanks,

Alex

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