From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hannes Frederic Sowa Subject: Re: [PATCH net-next] sock: don't enable netstamp for af_unix sockets Date: Tue, 27 Oct 2015 12:15:16 +0100 Message-ID: <1445944516.1337466.421368457.2463FECE@webmail.messagingengine.com> References: <1445863897-22646-1-git-send-email-hannes@stressinduktion.org> <20151026131928.GA1820@netboy> <1445866379.133031.420389177.3AE9E175@webmail.messagingengine.com> <20151027101157.GA1850@netboy> <1445944161.1336457.421364569.5449BCCB@webmail.messagingengine.com> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, Jesper Dangaard Brouer To: Richard Cochran Return-path: Received: from out4-smtp.messagingengine.com ([66.111.4.28]:40367 "EHLO out4-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751170AbbJ0LPQ (ORCPT ); Tue, 27 Oct 2015 07:15:16 -0400 Received: from compute1.internal (compute1.nyi.internal [10.202.2.41]) by mailout.nyi.internal (Postfix) with ESMTP id 5F836209E1 for ; Tue, 27 Oct 2015 07:15:16 -0400 (EDT) In-Reply-To: <1445944161.1336457.421364569.5449BCCB@webmail.messagingengine.com> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, Oct 27, 2015, at 12:09, Hannes Frederic Sowa wrote: > 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. 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? ;) Bye, Hannes