Re: [PATCH 1/3] Separate IRQ-stacks from 4K-stacks option

[Lee Revell]

On Sun, 2004-09-12 at 16:33, Andrea Arcangeli wrote:
> On Sun, Sep 12, 2004 at 09:35:42PM +0200, Ingo Molnar wrote:
> > no. A 2 msec nonpreemptable delay is a 2 msec delay, irqs on or off
> > alike.
> 
> irq-latency is an order of magnitude higher prio, than the scheduler
> latency. above you only talk about scheduler latency.
> 

But in this case the hardirq handler can run for 2ms, which caused a
scheduler latency problem, because nothing could run but other IRQs. 
The IRQ threading in Ingo's patches solves the problem, and seems to me
to be the correct solution.

> hence I don't think not allowing nested irqs at all is a good idea and
> it's a nice feature to support them.

Agreed.  I was just pointing out that in addition to being a bad idea it
wouldn't work unless the IDE i/o completion issue is addressed.

The issue IIRC was the potential for stack overflow with 4K stacks if we
get deeply nested IRQs.  I believe the VP patches allow you to see the
IRQ nesting in the logs, you could probably grep the logs for these
incidents.

Seems like you could test the stack overflow theory by setting up a
stream of interrupts from the sound card and RTC to coincide with the
timer interrupt, then stressing the disks and network.

Lee



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