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

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Message-ID: <p737in19kxw.fsf@bingen.suse.de>
Date:	08 Sep 2007 18:32:59 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	James Chapman <jchapman@...alix.com>
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

James Chapman <jchapman@...alix.com> writes:
> 
> Clearly, keeping a device in polled mode for 1-2 jiffies 

1-2 jiffies can be a long time on a HZ=100 kernel (20ms). A fast CPU
could do a lot of loops in this time, which would be waste of power
and CPU time.

On some platforms the precise timers (like ktime_get()) can be slow,
but often they are fast.  It might make sense to use a shorter
constant time wait on those with fast timers at least. Right now this
cannot be known by portable code, but there was a proposal some time
ago to export some global estimate to tell how fast
ktime_get().et.al. are. That could be reviewed.

-Andi
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