Re: [RFC PATCH 3/4] KVM: x86: Add EOI exit bitmap inference

From: Paolo Bonzini <pbonzini@redhat.com>
To: Jan Kiszka <jan.kiszka@siemens.com>,
	Steve Rutherford <srutherford@google.com>,
	kvm@vger.kernel.org
Cc: ahonig@google.com
Subject: Re: [RFC PATCH 3/4] KVM: x86: Add EOI exit bitmap inference
Date: Wed, 13 May 2015 11:24:19 +0200	[thread overview]
Message-ID: <55531843.9090304@redhat.com> (raw)
In-Reply-To: <55530702.5000407@siemens.com>

On 13/05/2015 10:10, Jan Kiszka wrote:
>>> >> There can even be multiple IOAPICs (thanks to your patches overcoming
>>> >> the single in-kernel instance).
>> > 
>> > With multiple IOAPICs you have more than 24 GSIs per IOAPIC.  That means
> I don't think that the number of pins per IOAPIC increases. At least not
> in the devices I've seen so far.

Sorry, that was supposed to be "more than 24 GSIs for the IOAPICs".

>> > that the above loop is broken for multiple IOAPICs.
> The worst case remains #IOAPIC * 24 iterations - if we have means to
> stop after the IOAPIC entries, not iterating over all routes.

Yes.  Which is not too bad if VCPUs can process it in parallel.

>> > But perhaps when enabling KVM_SPLIT_IRQCHIP we can use args[0] to pass
>> > the number of IOAPIC routes that will cause EOI exits?
> And you need to ensure that their routes can be found in the table
> directly. Given IOAPIC hotplug, that may not be the first ones there...

Can you reserve a bunch of GSIs at the beginning of the GSI space, and
use rt->map[] to access them and build the EOI exit bitmap?

Paolo