Re: Linux 2.6.20-rc6 - sky2 resume breakage

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Ingo Molnar wrote:
i'm wondering, could we go with Thomas' temporary patch that disables sky2 MSI if CONFIG_PM is enabled - we could revert that after 2.6.20. It's not like MSI is a life and death feature. On IO-APIC systems vectors are abundant and in any case we share irqs just fine. The true advantage of MSI is minimal. (MSI-X has the potential to be better by being message based, but in reality it still goes through the full IRQ layer.) MSI might be useful on really, really large systems - but i really hope those really large systems dont rely on CONFIG_PM. Meanwhile Thomas' patch maximizes the amount of working hardware (it has the chance to produce working systems in 100% of the cases) - which is a few orders of magnitude more important than IRQ management micro-costs. Am i missing anything?


Sharing irqs /sucks/. I routinely have to fight a USB device dying, because the ATA device is causing an interrupt storm, or vice versa. /Very/ common headache.

Other than that, they use a tiny bit fewer CPU cycles, and allow simplification of the interrupt handler (saving another few CPU cycles).

The biggest benefit is (a) for hardware designers, where MSI means a cleaner h/w design, and (b) preparation of drivers and the kernel systems for MSI-only hardware.

At present only high end hardware is MSI-only (like infiniband), but that's the future direction.

	Jeff


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