netdev - Re: [PATCH net-next] sock: don't enable netstamp for af

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Message-ID: <1445955309.7476.19.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Tue, 27 Oct 2015 07:15:09 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Richard Cochran <richardcochran@...il.com>, netdev@...r.kernel.org,
	Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH net-next] sock: don't enable netstamp for af_unix sockets

On Tue, 2015-10-27 at 14:44 +0100, Hannes Frederic Sowa wrote:
> 
> On Tue, Oct 27, 2015, at 14:19, Eric Dumazet wrote:
> > On Tue, 2015-10-27 at 12:15 +0100, Hannes Frederic Sowa wrote:
> > 
> > > Also counter question: why is the netstamp code protected by a
> > > static_key otherwise if not for trying to suppress the code path as
> > > often as possible if not used? ;)
> > 
> > Any idea of why timestamping is asked on AF_UNIX in the first place ?
> 
> I guess syslog code want's to have more accurate timetstamps on when the
> packet is send.
> 
> > For messages sent/received on af_unix sockets, in which place timestamp
> > is taken ?
> 
> in unix_sendmsg on the sending unix socket (we check peer unix socket
> for timestamp flag).
> 
> > Is it at the time skb is cooked and stored in receive queue, or the time
> > it was dequeued ?
> 
> No, at time it is send by sendmsg on the sending socket.
> 
> > In any case, is your patch changing af_unix behavior ? It is not clear
> > from your changelog...
> 
> No, af_unix logic does not pass this logic at all, so we don't need to
> care about netstamp code. netstamp_needed is private to dev.c.

Thanks for clarifying

Acked-by: Eric Dumazet <edumazet@...gle.com>


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