From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH net-next 17/17] tcp: get rid of two unnecessary u16s in TCP skb flags copying Date: Sat, 28 Feb 2009 19:08:45 -0800 (PST) Message-ID: <20090228.190845.137313353.davem@davemloft.net> References: <12358322833023-git-send-email-ilpo.jarvinen@helsinki.fi> <12358322832837-git-send-email-ilpo.jarvinen@helsinki.fi> <87ocwm0xx5.fsf@basil.nowhere.org> Mime-Version: 1.0 Content-Type: Text/Plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: ilpo.jarvinen@helsinki.fi, netdev@vger.kernel.org To: andi@firstfloor.org Return-path: Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:57480 "EHLO sunset.davemloft.net" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1755251AbZCADJE convert rfc822-to-8bit (ORCPT ); Sat, 28 Feb 2009 22:09:04 -0500 In-Reply-To: <87ocwm0xx5.fsf@basil.nowhere.org> Sender: netdev-owner@vger.kernel.org List-ID: =46rom: Andi Kleen Date: Sun, 01 Mar 2009 03:39:02 +0100 > "Ilpo J=E4rvinen" writes: >=20 > > From: Ilpo J=C3=A4rvinen > > > > I guess these fields were one day 16-bit in the struct but > > nowadays they're just using 8 bits anyway. > > > > This is just a precaution, didn't result any change in my > > case but who knows what all those varying gcc versions & > > options do. I've been told that 16-bit is not so nice with > > some cpus. >=20 > Typically when 16bit is not nice, 8bit isn't nice either. > For general flags the most save in terms of uniform performance > is "int" It's really only the truly ancient alpha cpus where this is a measurable issue. Those chips only have 32-bit loads and stores, so ever sub-32-bit access involves a 32-bit load/store and a bunch of byte extraction instructions. I don't think it's a relevant concern today. Especially on x86 if that's why you are alluding to Andi.