Matthew Wilcox wrote:
On Fri, Jul 11, 2008 at 01:50:23PM +0900, Kenji Kaneshige wrote:
I'm very sorry for very delayed comment, but I have a concern
about irq affinity code. Since I didn't have enough time to
look at your patch, I might be misunderstanding something...
In my understanding, when irq affinity is changed on one of
the IRQs corresponding to MSI, it will not completed until
interrupts occur on all the IRQs. Attempts to change irq
affinity before previous affinity change is finished will be
ignored. Here, suppose that device uses three MSI irqs. In
this case, your patch manages four irqs, but only three
interrupts are used. If irq affinity changed on this MSI
interrupts, will it be completed?
I have tested the affinity code with an ICH9 AHCI:
495: 117233 117966 118033 117797 PCI-MSI-edge ahci
496: 29860 29106 30191 28705 PCI-MSI-edge ahci
497: 0 0 0 0 PCI-MSI-edge ahci
498: 0 0 0 0 PCI-MSI-edge ahci
499: 0 0 0 0 PCI-MSI-edge ahci
500: 0 0 0 0 PCI-MSI-edge ahci
This chip requires 16 MSIs to be registered, and it has 6 ports.
Only ports 0 and 1 have a device attached. If I change the mask of
an active irq (eg 495 or 496), it takes effect on both of them. If I
change the mask of an inactive irq (497-500), nothing happens. But I
can subsequently change the mask on 495 or 496 successfully.
I can't tell you why this works this way; I haven't looked in enough
detail at the irq affinity code, but this is my observation.
What I was worrying about was around irq_cfg->move_in_progress.
Since your environment has less than 8 cpus according to your
/proc/interrupts, I think your environment seems to use "apic_flat"
mode for interrupt handling. In this case, irq_cfg->move_in_progress
is not used for irq migration. I think this is why your environment
didn't encounter the problem I worried about. We should note that
vector allocation logic varies depending on the environment.
BTW, I looked at your take 4 patch. The problem I worried about
seems not to exist in this version (as a good side effect).
Thanks,
Kenji Kaneshige
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