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

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Date:	Thu, 30 Jun 2011 10:52:42 -0700
From:	"Wyborny, Carolyn" <carolyn.wyborny@...el.com>
To:	Ben Hutchings <bhutchings@...arflare.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.



>-----Original Message-----
>From: Ben Hutchings [mailto:bhutchings@...arflare.com]
>Sent: Tuesday, June 21, 2011 10:38 AM
>To: Wyborny, Carolyn
>Cc: David Miller; 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.

I will try to do this.  Confirming you are suggesting a replacement or an alternate for the current -c/-C coalesce settings with perhaps some room reserved for some future coalescing type features and enable settings per queue?  I agree they are related and initially considered trying to add DMAC to the current coalescing settings, but they are full.

Carolyn

Carolyn Wyborny
Linux Development
LAN Access Division
Intel Corporation