netdev - Re: MSI interrupts and disable

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Message-ID: <86802c440710161101o34a1b982w95c7473f0ec744ed@mail.gmail.com>
Date:	Tue, 16 Oct 2007 11:01:35 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Jeff Garzik" <jgarzik@...ox.com>
Cc:	"Manfred Spraul" <manfred@...orfullife.com>,
	"Ayaz Abdulla" <aabdulla@...dia.com>,
	nedev <netdev@...r.kernel.org>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"David Miller" <davem@...emloft.net>,
	"Andrew Morton" <akpm@...ux-foundation.org>
Subject: Re: MSI interrupts and disable_irq

On 10/16/07, Jeff Garzik <jgarzik@...ox.com> wrote:
> Yinghai Lu wrote:
> > On 10/15/07, Jeff Garzik <jgarzik@...ox.com> 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.

at this point, nic in mcp55 is using msi or INTx.

YH
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