Re: Linux 2.6.20-rc6 - sky2 resume breakage
From: Jeff Garzik
Date: Tue Jan 30 2007 - 02:39:31 EST
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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