From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754496AbbIQJDc (ORCPT ); Thu, 17 Sep 2015 05:03:32 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34997 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754212AbbIQJD3 (ORCPT ); Thu, 17 Sep 2015 05:03:29 -0400 From: Vitaly Kuznetsov To: David Miller Cc: David.Laight@ACULAB.COM, haiyangz@microsoft.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kys@microsoft.com, jasowang@redhat.com Subject: Re: [PATCH net-next RFC] net: increase LL_MAX_HEADER for Hyper-V References: <1442418625-11805-1-git-send-email-vkuznets@redhat.com> <063D6719AE5E284EB5DD2968C1650D6D1CB9800B@AcuExch.aculab.com> <20150916.105936.2275139635170756984.davem@davemloft.net> Date: Thu, 17 Sep 2015 11:03:25 +0200 In-Reply-To: <20150916.105936.2275139635170756984.davem@davemloft.net> (David Miller's message of "Wed, 16 Sep 2015 10:59:36 -0700 (PDT)") Message-ID: <87k2rpwh7m.fsf@vitty.brq.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org David Miller writes: > From: David Laight > Date: Wed, 16 Sep 2015 16:25:03 +0000 > >> Am I right in thinking this is adding an extra 96 unused bytes to the front >> of almost all skb just so that hyper-v can make its link level header >> contiguous with whatever follows (IP header ?). >> >> Doesn't sound ideal. > > Agreed, this is rediculous, and the entire stack will incur this cost > just because hyperv is enabled in the kernel config. That's what 'RFC' in the subject was about :-) We already have a precedent of increasing LL_MAX_HEADER globaly because of a config option (CONFIG_MAC80211_MESH) but Hyper-V needs more. -- Vitaly