netdev - Re: RFC: possible NAPI improvements to reduce interrupt rates for low traffic rates

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Message-ID: <46E01D16.5000609@katalix.com>
Date:	Thu, 06 Sep 2007 16:30:30 +0100
From:	James Chapman <jchapman@...alix.com>
To:	Stephen Hemminger <shemminger@...ux-foundation.org>
CC:	netdev@...r.kernel.org, hadi@...erus.ca, davem@...emloft.net,
	jeff@...zik.org, mandeep.baines@...il.com, ossthema@...ibm.com
Subject: Re: RFC: possible NAPI improvements to reduce interrupt rates for
 low traffic rates

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?

> 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 
based on settings like CONFIG_PREEMPT, CONFIG_HIGH_RES_TIMER, CONFIG_HZ 
and maybe even bogomips / nr_cpus.

-- 
James Chapman
Katalix Systems Ltd
http://www.katalix.com
Catalysts for your Embedded Linux software development

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