netdev - Re: [PATCH 2/4] e1000: add module option to set transmit descriptor size

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Message-ID: <20080627145522.GB8991@ajones-laptop.nbttech.com>
Date:	Fri, 27 Jun 2008 07:55:22 -0700
From:	Arthur Jones <ajones@...erbed.com>
To:	Jeff Garzik <jeff@...zik.org>
CC:	Andy Gospodarek <andy@...yhouse.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"jeffrey.t.kirsher@...el.com" <jeffrey.t.kirsher@...el.com>,
	"jesse.brandeburg@...el.com" <jesse.brandeburg@...el.com>
Subject: Re: [PATCH 2/4] e1000: add module option to set transmit descriptor
	size

Hi Jeff, ...

On Fri, Jun 27, 2008 at 07:21:22AM -0700, Arthur Jones wrote:
> On Thu, Jun 26, 2008 at 10:10:37PM -0700, Jeff Garzik wrote:
> > Andy Gospodarek wrote:
> > > This patch added the TxDescPower parameter to the e1000 module.  This
> > > parameter represents the size-order of each transmit descriptor.  The
> > > valid size for descriptors would be 2^7 (128) - 2^12 (4096) bytes each.
> > > As this value decreases one may want to consider increasing the
> > > TxDescriptors value to maintain the same amount of frame memory.  This
> > > patch does not change the defaults for any particular hardware model, so
> > > this will not have an effect on existing users.
> > [...]
> > I don't see why a module parameter is needed.  In practice, nobody will
> > ever think about this option, much less use it.

One thing that may not be immediately obvious is
that setting the descriptor payload size low to avoid
the chip bug has a very negative effect on performance.
I don't want to lower the descriptor payload size
unless I absolutely have to -- e.g. environments where
link flap on chip reset causes major distruptions to the
network...

Arthur
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