netdev - RE: [RFC 2/2] ethtool: Add support for DMA Coalescing feature config to ethtool.

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Date:	Tue, 21 Jun 2011 18:38:13 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	"Wyborny, Carolyn" <carolyn.wyborny@...el.com>
Cc:	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [RFC 2/2] ethtool: Add support for DMA Coalescing feature
 config to ethtool.

On Tue, 2011-06-21 at 10:23 -0700, Wyborny, Carolyn wrote:
> 
> >-----Original Message-----
> >From: David Miller [mailto:davem@...emloft.net]
> >Sent: Friday, June 17, 2011 11:54 AM
> >To: Wyborny, Carolyn
> >Cc: netdev@...r.kernel.org; bhutchings@...arflare.com
> >Subject: Re: [RFC 2/2] ethtool: Add support for DMA Coalescing feature
> >config to ethtool.
> >
> >From: "Wyborny, Carolyn" <carolyn.wyborny@...el.com>
> >Date: Fri, 17 Jun 2011 08:50:11 -0700
> >
> >> I will add a fuller description of the feature in my updated patch.
> >> I thought the feature was more well known. Quick description is that
> >> it's a power saving feature that causes the adapter to coalesce its
> >> DMA writes at low traffic times to save power on the platform by
> >> reducing wakeups.  The parameter is intended as a simple u32 value,
> >> not just an on or off, but also to allow a variety of configuration
> >> by adapter vendors, with validation of the input on the driver side.
> >> Since I left out the implementation in my patch, this wasn't clear.
> >> I will also fix this in my next submission.
> >
> >The value cannot have adapter specific meaning, you must define it
> >precisely and in a generic manner, such that the user can specify the
> >same setting across different card types.
> 
> Ok, good point.  I will refine the definition of the parameter in the
> next submission, once the dust clears on the major revisions in
> progress.

You may wish to propose a new command structure that covers both IRQ and
DMA moderation.  They seem to be related, since DMA cannot be delayed
longer than the corresponding IRQ.  We are currently lacking a way to
specify different IRQ moderation for multiqueue devices where the queues
are not all used in the same way.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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