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SubjectRe: is irq smp affinity good for anything?
On Tue, Mar 11, 2003 at 08:48:59PM -0500, Mark Hahn wrote:
> > I did not expect to increase global latency to these results...
> > and neither to increase latency in the CPU that's receiving
> > just one interrupt!
> but isn't that just a cache effect? that is, you're keeping
> all cpus busy (caches too) with user-space, so when the interrupt
> comes in, a bound interrupt has no choice, even if the cache
> is busy with userspace.

first of all thanks for your reply,

I think that user space code always has to make the best use of cache as it
can... in other words, i don't want to use a cpu exclusively for a device
that delivers 6000 ints/second

I bound an irq to a cpu because I thought that:

as spin_irq_locks just disables interrupts locally I should get better
latency that just one ISR on that particular cpu could at least reduce
a little the number of times that interrupts get disabled on that cpu

... that was my reasoning...

but latency gets worse... that's not comphrensible for me...


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