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Date:	Thu, 6 Sep 2007 16:37:03 +0100
From:	Stephen Hemminger <>
To:	James Chapman <>
Subject: Re: RFC: possible NAPI improvements to reduce interrupt rates for
 low traffic rates

On Thu, 06 Sep 2007 16:30:30 +0100
James Chapman <> wrote:

> Stephen Hemminger wrote:
> > What about the latency that NAPI imposes? Right now there are certain applications that
> > don't like NAPI because it add several more microseconds, and this may make it worse.
> Latency is something that I think this approach will actually improve, 
> at the expense of additional polling. Or is it the ksoftirqd scheduling 
> latency that you are referring to?

The problem is that you leave interrupts disabled, right. Also you are busy during
idle which kills powersaving and no hz clock.

> > Maybe a per-device flag or tuning parameters (like weight sysfs value)? or some other
> > way to set low-latency values.
> Yes. I'd like to think good defaults could be derived though, perhaps 
> and maybe even bogomips / nr_cpus.
> -- 
> James Chapman
> Katalix Systems Ltd
> Catalysts for your Embedded Linux software development
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