Re: [Xen-devel] Re: [PATCH 1/2] xen: events: do not workaround too-small nr_irqs

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2011-02-15 at 15:15 +0000, Ian Campbell wrote:
> On Wed, 2011-02-09 at 16:21 +0000, Konrad Rzeszutek Wilk wrote:
> > On Wed, Feb 09, 2011 at 11:10:44AM +0000, Ian Campbell wrote:
> > > This workaround was somewhat useful prior to the introduction of the
> > > core irq allocator and 026c9d2d0d75 "xen: events: allocate GSIs and
> > > dynamic IRQs from separate IRQ ranges." but should not be unnecessary now.
> > > 
> > > If nr_irqs turns out to be too small under Xen then we use (or define
> > > if necessary) the interfaces to increase nr_irqs rather than working
> > > around the core allocator in this way.
> > > 
> > > In my configuration NR_IRQS ends up being 2304 with nr_irq_gsi 272
> > > which is sufficient.
> > 
> > Is this configuration where you run Xen + Linux under QEMU?
> 
> I've just tried these two patches under qemu, booting a 64 bit
> xen-unstable hypervisor with a 32 bit domain 0 kernel, pxeboot using:
>         qemu-system-x86_64 -m 256 -vnc 0.0.0.0:1 -k en-gb -serial stdio -boot 
> nc \
>               -usb -usbdevice tablet -net 
> nic,vlan=0,macaddr=00:16:3e:f7:c4:1d,model=e1000 \
>               -net tap,vlan=0,ifname=tapQEMU.0 -hda /dev/VG/debian-HVM-1 
>         
> There I appear to get:
>         nr_irqs_gsi: 272
>         NR_IRQS:2304 nr_irqs:256 16
> 
> which leads to a failure due to not being able to allocate a dynamic IRQ
> (because 272 > 256!), I'll dig into this...

The solution is to increase nr_irqs, which is currently static after
boot even with sparseirqs.

Fortunately tglx intends to make this dynamically growable in the IRQ
core in the 2.6.39 time frame which nicely ties in with this patch.

Ian.


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