netdev - Re: [PATCH] net-packet: tx timestamping on tpacket ring

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Date:	Mon, 15 Apr 2013 12:37:52 -0400
From:	Willem de Bruijn <willemb@...gle.com>
To:	Paul Chavent <Paul.Chavent@...ra.fr>
Cc:	Richard Cochran <richardcochran@...il.com>,
	Eric Dumazet <edumazet@...gle.com>,
	daniel.borkmann@....ee.ethz.ch, xemul@...allels.com,
	ebiederm@...ssion.com, netdev@...r.kernel.org
Subject: Re: [PATCH] net-packet: tx timestamping on tpacket ring

On Mon, Apr 15, 2013 at 3:31 AM, Paul Chavent <Paul.Chavent@...ra.fr> wrote:
> Hi.
>
>
> On 04/13/2013 08:56 PM, Willem de Bruijn wrote:
>>
>> [...]
>>
>> --- a/net/core/skbuff.c
>> +++ b/net/core/skbuff.c
>> @@ -3311,7 +3311,7 @@ void skb_tstamp_tx(struct sk_buff *orig_skb,
>>                  * so keep the shared tx_flags and only
>>                  * store software time stamp
>>                  */
>> -               skb->tstamp = ktime_get_real();
>> +               orig_skb->tstamp = skb->tstamp = ktime_get_real();
>>         }
>
>
> You said that "the orig_skb is usually freed shortly after
> skb_tstamp_tx is called".
>
> So i suppose that if you had coded it, that's because this orig_skb is the
> one that is given to the skb destructor. So when you call
> __packet_set_timestamp, in tpacket_destruct_skb, you get this timestamp ? Am
> i right ?
>
>
> Why we couldn't call
> *skb_hwtstamps(orig_skb) = *skb_hwtstamps(skb) = *hwtstamps;
> in order to get the hardware timestamping too ?

Probably. That would also answer Daniel's question to the same
functionality. I'm a bit less familiar with the hardware path, so will
read up before just submitting it.

> Thank for your help.
>
> Paul.
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