Re: [PATCH v6] kvm: Use a bitmap for tracking used GSIs

From: Alex Williamson <alex.williamson@hp.com>
To: Avi Kivity <avi@redhat.com>
Cc: kvm@vger.kernel.org, sheng.yang@intel.com, mst@redhat.com
Subject: Re: [PATCH v6] kvm: Use a bitmap for tracking used GSIs
Date: Mon, 18 May 2009 16:32:23 -0600	[thread overview]
Message-ID: <1242685943.4700.102.camel@lappy> (raw)
In-Reply-To: <4A10798E.4030301@redhat.com>

On Sun, 2009-05-17 at 23:54 +0300, Avi Kivity wrote:
> Alex Williamson wrote:
> > We're currently using a counter to track the most recent GSI we've
> > handed out.  This quickly hits KVM_MAX_IRQ_ROUTES when using device
> > assignment with a driver that regularly toggles the MSI enable bit.
> > This can mean only a few minutes of usable run time.  Instead, track
> > used GSIs in a bitmap.
> >
> >  v6: Make use of ALIGN macro, per Michael
> >      Define KVM_IOAPIC_NUM_PINS if not already, per Michael
> >   
> 
> Due to me being slow I nacked this after you prepared the new patch.  Sorry.
> 
> We could define have platform_gsis passed from qemu to tell us how many 
> GSIs to reserve (let's pretend libkvm isn't on death row for a moment).

Perhaps we should update the bitmap on entry points that everyone uses
so we don't have to worry about preallocating.  We could set the bitmap
in kvm_add_routing_entry() and clear it in kvm_del_routing_entry().
This would mean that kvm_del_routing_entry() implicitly gives up a GSI
obtained via kvm_get_irq_route_gsi(), which seems to be the assumption
already.

That would eliminate any need for proliferating KVM_CAP_IRQ_ROUTING
ifdefs or doing anything based on KVM_IOAPIC_NUM_PINS, but should I keep
the KVM_CAP_IRQ_ROUTING around the new code for documentation purposes?
Thanks,

Alex