netdev - Re: via-rhine interrupts

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Message-ID: <20100819170912.GA2387@del.dom.local>
Date:	Thu, 19 Aug 2010 19:09:12 +0200
From:	Jarek Poplawski <jarkao2@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	ruzicka.jakub@...il.com, netdev@...r.kernel.org
Subject: Re: via-rhine interrupts

On Wed, Aug 18, 2010 at 11:49:39PM -0700, David Miller wrote:
> From: Jarek Poplawski <jarkao2@...il.com>
> Date: Sun, 15 Aug 2010 22:04:31 +0200
> 
> > I've just tested it using a simplistic patch below, which skips
> > some napi receiving by doing it only every second jiffie (on even
> > ones), and I've got around 30% less interrupts from via-rhine,
> > which seems to suggest napi works OK, but there is too low
> > traffic (or too fast soft interrupt handling) to affect hard
> > interrupts. (Btw, probably CONFIG_HZ can matter here a bit too.
> > I tested with 1000.)
> 
> 100Mbit on any modern system isn't going to trigger NAPI much at all
> even with near full link utilization.
> 
> The simply cpu processes the packets too fast for them to gather up
> much at all.
> 
> Some improvement in polling could be gained if the via-rhine has some
> HW interrupt mitigation settings.  However after a quick perusal of
> the driver I don't see anything about this.  The mitigation ethtool
> ops aren't implemented either, so I'm not optimistic :-)
> 

Yes, now I see the old comments (pre 2.6.27) mentioned 10kpps
threshold, which wasn't reached in Jakub's example.

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=32b0f53e5bc80b87fd20d4d78a0e0cb602c9157a

Jarek P.
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