netdev - Re: [net-next PATCH] igb: remove skb

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Date:	Thu, 26 Feb 2009 04:24:06 -0800
From:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>
To:	David Miller <davem@...emloft.net>,
	"Tantilov, Emil S" <emil.s.tantilov@...el.com>,
	Patrick Ohly <patrick.ohly@...el.com>
Cc:	netdev@...r.kernel.org, gospo@...hat.com,
	alexander.h.duyck@...el.com, mitch.a.williams@...el.com
Subject: Re: [net-next PATCH] igb: remove skb_orphan calls

On Thu, Feb 26, 2009 at 4:14 AM, David Miller <davem@...emloft.net> wrote:
> From: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
> Date: Thu, 26 Feb 2009 02:46:23 -0800
>
>> From: Alexander Duyck <alexander.h.duyck@...el.com>
>>
>> The skb_orphan call in the tx path has been shown to cause issues as seen
>> with the workarounds required for timestamping.
>>
>> In order to avoid this it is easiest just to remove the skb_orphan call as
>> the motivation for including it was purely performance based, and the
>> overall gain from having the call was minimal.
>>
>> Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>
>> Acked-by: Mitch Williams <mitch.a.williams@...el.com>
>> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
>
> While I'm happy to apply this, I don't see it as helping the
> timestamping situation.
>
> All someone has to do is enable the new timestamping on loopback to
> trigger the problem, the loopback MUST orphan SKBs before it pushes
> them back into the stack for receive.
>
> Also, Herbert and I have talked about orphaning SKBs even earlier than
> dev_queue_xmit()
>
> This post-send timestamping scheme is not going to work, is poorly
> designed, and needs to be completely rearchitected.
>
> If it isn't fixed soon, I'll have no choice but to completely revert
> all of the timestamping stuff.
> --
>

Adding Emil and Patrick.

While no issues were seen in testing, I will verify with Emil that
loopback testing was done.  Also I will work with Patrick to ensure
that we resolve any issues with lookback and timestamping.

-- 
Cheers,
Jeff
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