Re: MSI interrupts and disable_irq

[Jeff Garzik]

Yinghai Lu wrote:
> On 10/15/07, Jeff Garzik <jgarzik@xxxxxxxxx> wrote:
> > Manfred Spraul wrote:
> > > Jeff Garzik wrote:
> > > > I think the scenario you outline is an illustration of the approach's
> > > > fragility:  disable_irq() is a heavy hammer that originated with INTx,
> > > > and it relies on a chip-specific disable method (kernel/irq/manage.c)
> > > > that practically guarantees behavior will vary across MSI/INTx/etc.
> > > I checked the code: IRQ_DISABLE is implemented in software, i.e.
> > > handle_level_irq() only calls handle_IRQ_event() [and then the nic irq
> > > handler] if IRQ_DISABLE is not set.
> > > OTHO: The last trace looks as if nv_do_nic_poll() is interrupted by an irq.
> > >
> > > Perhaps something corrupts dev->irq? The irq is requested with
> > >    request_irq(np->pci_dev->irq, handler, IRQF_SHARED, dev->name, dev)
> > > and disabled with
> > >    disable_irq_lockdep(dev->irq);
> > >
> > > Someone around with a MSI capable board? The forcedeth driver does
> > >    dev->irq = pci_dev->irq
> > > in nv_probe(), especially before pci_enable_msi().
> > > Does pci_enable_msi() change pci_dev->irq? Then we would disable the
> > > wrong interrupt....
> > Remember, fundamentally MSI-X is a one-to-many relationship, when you
> > consider a single PCI device might have multiple vectors.
>
> msi-x is using other entry
>
>                if (np->msi_flags & NV_MSI_X_ENABLED)
>
> enable_irq_lockdep(np->msi_x_entry[NV_MSI_X_VECTOR_ALL].vector);

Correct, but the overall point was that MSI-X conceptually conflicts 
with the existing "lockless" disable_irq() schedule, which was written 
when there was a one-one relationship between irq, PCI device, and work 
to be done.

	Jeff



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