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Date: Sat, 4 Jan 2003 16:23:54 +0100 (CET)
From: Steffen Persvold <sp@scali.com>
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To: "David S. Miller" <davem@redhat.com>,
       Jeff Garzik <jgarzik@mandrakesoft.com>, <linux-kernel@vger.kernel.org>
Subject: NAPI and tg3
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Hi guys,

I have access to 8 Dell 2650s with onboard Broadcom BCM5701 chips. They 
are quipped with Dual 2.4 GHz Xeon processors and 1GB of RAM. I'm running 
RedHat 7.3, but with a stock 2.4.20 kernel.

As I understand it the tg3 driver is using NAPI on the 2.4.20 kernel 
(dev->poll). I've been experiencing bad performance (low bandwidth) on 
cluster applications running with LAM for example, but the problem 
manifest itself if you run two bandwidth needy applications in parallel 
on two machines (i.e two processes on each machine, one per processor) 
using Gbe. 

I've disabled the NAPI mode and went back to the old interrupt method and 
this works much better (i.e the bandwidth is now evenly distributed 
between the two applications).

What could be the cause of this problem ? Is it NAPI itself (doing RX 
under scheduler control) or is it something else (for example lock 
contetion).

Any ideas ?

Thanks,
-- 
  Steffen Persvold   |       Scali AS      
 mailto:sp@scali.com |  http://www.scali.com
Tel: (+47) 2262 8950 |   Olaf Helsets vei 6
Fax: (+47) 2262 8951 |   N0621 Oslo, NORWAY


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