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

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Message-ID: <5059D836.8020205@redhat.com>
Date:	Wed, 19 Sep 2012 17:35:34 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Alex Williamson <alex.williamson@...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 09/19/2012 04:54 PM, Alex Williamson wrote:
> 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.

Ok.  I tried to see if it would fit in the routing table, but rcu means
that we'll need to have the resampler as a pointer, not a field, and
that we'll need to migrate it to the new array when rebuilt.  So it ends
up not being any simpler.


-- 
error compiling committee.c: too many arguments to function
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