From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefano Brivio Subject: Re: [PATCH net 1/2] geneve, vxlan: Don't check skb_dst() twice Date: Mon, 15 Oct 2018 13:08:30 +0200 Message-ID: <20181015130830.1c177301@redhat.com> References: <61596775-4b5f-884a-7a0d-d8c134bb7e8a@6wind.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Cc: "David S. Miller" , Xin Long , Sabrina Dubroca , netdev@vger.kernel.org To: Nicolas Dichtel Return-path: Received: from mx1.redhat.com ([209.132.183.28]:42376 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726357AbeJOSxY (ORCPT ); Mon, 15 Oct 2018 14:53:24 -0400 In-Reply-To: <61596775-4b5f-884a-7a0d-d8c134bb7e8a@6wind.com> Sender: netdev-owner@vger.kernel.org List-ID: On Mon, 15 Oct 2018 12:19:41 +0200 Nicolas Dichtel wrote: > Le 12/10/2018 à 23:53, Stefano Brivio a écrit : > > Commit f15ca723c1eb ("net: don't call update_pmtu unconditionally") avoids > > that we try updating PMTU for a non-existent destination, but didn't clean > > up cases where the check was already explicit. Drop those redundant checks. > Yes, I leave them to avoid calculating the new mtu value when not needed. We are > in the xmit path. Before 2/2 of this series, though, we call skb_dst_update_pmtu() (and in turn dst->ops->update_pmtu()) for *every* packet with a dst, which I'd dare saying is by far the most common case. Besides, 2/2 needs anyway to calculate the MTU to fix a bug. So I think this is a vast improvement overall. If we want to improve this further and avoid any indirect calls in the most common path, we would need to cache the MTU in the dst -- it's probably doable, but I would fix the specific issue addressed by 2/2 first. -- Stefano