Re: User mode drivers: part 1, interrupt handling (patch for 2.6.11)

From: Peter Chubb
Date: Sun Mar 13 2005 - 19:39:48 EST

>>>>> "Jon" == Jon Smirl <jonsmirl@xxxxxxxxx> writes:

Jon> On Fri, 11 Mar 2005 14:36:10 +1100, Peter Chubb
Jon> <peterc@xxxxxxxxxxxxxxxxxx> wrote:
>> As many of you will be aware, we've been working on infrastructure
>> for user-mode PCI and other drivers. The first step is to be able
>> to handle interrupts from user space. Subsequent patches add
>> infrastructure for setting up DMA for PCI devices.

Jon> I've tried implementing this before and could not get around the
Jon> interrupt problem. Most interrupts on the x86 architecture are
Jon> shared. Disabling the IRQ at the PIC blocks all of the shared

Fortunately, most interrupts on IA64, ARM, etc., are unshared. And
with PCI-Express, the problem will go away. Even on X86, things
aren't all bad: one can usually find a PCI slot which doesn't share
interrupts with anything you care about.

The scenario I'm thinking about with these patches are things like
low-latency user-level networking between nodes in a cluster, where
for good performance even with a kernel driver you don't want to share
your interrupt line with anything else.

Dr Peter Chubb peterc AT
The technical we do immediately, the political takes *forever*
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