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Date: Wed, 12 Mar 2003 11:11:16 +0100
To: Mark Hahn <hahn@physics.mcmaster.ca>
Cc: linux-kernel@vger.kernel.org
Subject: Re: is irq smp affinity good for anything?
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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.
Hi

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...

	Ulisses


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