Messages in this thread | | | Date | Tue, 3 Feb 2009 20:53:04 +0100 | From | Ingo Molnar <> | Subject | Re: Reworking suspend-resume sequence (was: Re: PCI PM: Restore standard config registers of all devices early) |
| |
* Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Tue, 3 Feb 2009, Ingo Molnar wrote: > > > > > > I'm really not sure why that handle_edge_irq thing uses "ack_and_mask()" > > > instead of just "desc->chip->ack()"? I'm also totally flummoxed as to why > > > it feels it needs to go all the way out to the device to mask things, > > > instead of just masking at an apic level, which is much simpler and faster > > > (especially since masking should never happen in practice anyway). > > > > Hm, do you mean mask_ack_irq()? > > Yes. > > > The ->mask_ack() irqchip method is just a > > small tweak normally: if we get an irq while the irq was disabled, we can > > mark it pending and masks it for real. > > No, I know why mask_ack_irq() does what it does and I agree with it. What > I was really reacting to was that handle_edge_irq() calls it at _all_. > IOW, I'm talking about this code: > > handle_edge_irq(unsigned int irq, struct irq_desc *desc) > ... > if (unlikely((desc->status & (IRQ_INPROGRESS | IRQ_DISABLED)) || > !desc->action)) { > desc->status |= (IRQ_PENDING | IRQ_MASKED); > mask_ack_irq(desc, irq); > .. > > where the masking part seems a bit pointless. And in the case of MSI, it > causes us to go all the way out to the device, which sounds pretty > expensive too.
hm, i agree that your patched version looks much simpler.
There's two reasons we have this variant:
- huge bikeshed painting thread in the early days of the genirq patchset, with folks expressing concern about our original plans to keep edge-triggered unmasked _always_. (which your patch does too) So we just went with the path of least resistence and used this hybride.
- the screaming-irq observation i had - do you consider that valid?:
>> [ In theory this also solves screaming level-triggered irqs that >> advertise themselves as edge-triggered [due to firmware/BIOS bug - >> these do happen] and then keep spamming the system. ]
I wanted to have a pretty much interchangeable flow method between edge and level triggered - so that the BIOS cannot screw us by enumerating an irq as edge-triggered while it's level-triggered.
Especially for legacy x86 irqs in the low <16 range the trigger mode can be influenced by chipset settings and might not always be what we think it is.
That's my rough recollection - Thomas, is that correct and do you have anything to add here?
Ingo
| |