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

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Message-Id: <1445944161.1336457.421364569.5449BCCB@webmail.messagingengine.com>
Date:	Tue, 27 Oct 2015 12:09:21 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Richard Cochran <richardcochran@...il.com>
Cc:	netdev@...r.kernel.org, Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH net-next] sock: don't enable netstamp for af_unix sockets

Hi Richard,

On Tue, Oct 27, 2015, at 11:11, Richard Cochran wrote:
> On Mon, Oct 26, 2015 at 02:32:59PM +0100, Hannes Frederic Sowa wrote:
> > On Mon, Oct 26, 2015, at 14:19, Richard Cochran wrote:
> > > On Mon, Oct 26, 2015 at 01:51:37PM +0100, Hannes Frederic Sowa wrote:
> > > > netstamp_needed is toggled for all socket families if they request
> > > > timestamping. But some protocols don't need the lower-layer timestamping
> > > > code at all. This patch starts disabling it for af-unix.
> > > 
> > > What problem is this patch trying to solve?
> > 
> > netstamp_needed is a static-key which enables timestamping code in the
> > networking stack receive functions for every packet, while it is not
> > needed for AF_UNIX/LOCAL. So it is merely a small performance
> > enhancement.
> 
> Are there any numbers that show the effect of this enhancement?

I haven't personally done any performance numbers.

Jesper (in Cc) noticed that it showed up in perf performance reports
even though he used a very minimal setup. Turned out that
systemd-journald enables timestamping on AF_UNIX sockets which thus
enabled netstamps globally. I think Jesper can chime in here.

Bye,
Hannes
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