linux-kernel - Re: RFC: issues concerning the next NAPI interface

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Message-ID: <20070824213514.GL4282@austin.ibm.com>
Date:	Fri, 24 Aug 2007 16:35:14 -0500
From:	linas@...tin.ibm.com (Linas Vepstas)
To:	Jan-Bernd Themann <ossthema@...ibm.com>
Cc:	Bodo Eggert <7eggert@....de>, netdev <netdev@...r.kernel.org>,
	Thomas Klein <tklein@...ibm.com>,
	Jan-Bernd Themann <themann@...ibm.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-ppc <linuxppc-dev@...abs.org>,
	Christoph Raisch <raisch@...ibm.com>,
	Marcus Eder <meder@...ibm.com>,
	Stefan Roscher <stefan.roscher@...ibm.com>
Subject: Re: RFC: issues concerning the next NAPI interface

On Fri, Aug 24, 2007 at 11:11:56PM +0200, Jan-Bernd Themann wrote:
> (when they are available for
> POWER in our case). 

hrtimer worked fine on the powerpc cell arch last summer.
I assume they work on p5 and p6 too, no ??

> I tried to implement something with "normal" timers, but the result
> was everything but great. The timers seem to be far too slow.
> I'm not sure if it helps to increase it from 1000HZ to 2500HZ
> or more.

Heh. Do the math. Even on 1gigabit cards, that's not enough:

(1gigabit/sec) x (byte/8 bits) x (packet/1500bytes) x (sec/1000 jiffy) 

is 83 packets a jiffy (for big packets, even more for small packets, 
and more again for 10 gigabit cards). So polling once per jiffy is a 
latency disaster.

--linas  

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