netdev - Re: [Cbe-oss-dev] [PATCH 12/15] spidernet: increase the NAPI weight

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Message-ID: <20070614220829.GX4397@austin.ibm.com>
Date:	Thu, 14 Jun 2007 17:08:29 -0500
From:	linas@...tin.ibm.com (Linas Vepstas)
To:	Arnd Bergmann <arnd@...db.de>
Cc:	cbe-oss-dev@...abs.org, netdev@...r.kernel.org,
	Jeff Garzik <jeff@...zik.org>
Subject: Re: [Cbe-oss-dev] [PATCH 12/15] spidernet: increase the NAPI weight

On Wed, Jun 13, 2007 at 10:49:51PM +0200, Arnd Bergmann wrote:
> On Wednesday 13 June 2007, Jeff Garzik wrote:
> > > +/* We really really want to empty the ring buffer every time,
> > > + * so as to avoid the RX ram full bug. So set te napi wieght
> > > + * to the ring size.
> > > + */
> > > +#define SPIDER_NET_NAPI_WEIGHT       SPIDER_NET_RX_DESCRIPTORS_DEFAULT
> > 
> > I don't see why spider_net should have a different NAPI weight from 
> > other drivers

It was a lame attempt to try to trick napi into draining the entire
RX queue in one go, with the goal of avoiding the dreaded rx ram full.
I'm not sure it made much of a difference, so we can let this slide.

> Would it help to do it the other way round, as in

No, that would shorten the RX queue, thus making it more likely
to overflow. At gigabit speeds, its petty easy to fill this thing
up multiple times per jiffy. The driver should continue to operate 
either way, but the larger queue should keep it from being a busy 
beaver.

--linas
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