From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966746AbeCAJKt (ORCPT ); Thu, 1 Mar 2018 04:10:49 -0500 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:54140 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S966675AbeCAJKq (ORCPT ); Thu, 1 Mar 2018 04:10:46 -0500 Date: Thu, 1 Mar 2018 10:10:38 +0100 From: Jesper Dangaard Brouer To: Jason Wang Cc: mst@redhat.com, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, john.fastabend@gmail.com, brouer@redhat.com Subject: Re: [PATCH net-next 0/2] virtio-net: re enable XDP_REDIRECT for mergeable buffer Message-ID: <20180301101038.4253424d@redhat.com> In-Reply-To: <1519874345-10235-1-git-send-email-jasowang@redhat.com> References: <1519874345-10235-1-git-send-email-jasowang@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 1 Mar 2018 11:19:03 +0800 Jason Wang wrote: > This series tries to re-enable XDP_REDIRECT for mergeable buffer which > was removed since commit 7324f5399b06 ("virtio_net: disable > XDP_REDIRECT in receive_mergeable() case"). Main concerns are: > > - not enough tailroom was reserved which breaks cpumap To address this at a more fundamental level, I would suggest that we/you instead extend XDP to know it's buffers "frame" size/end. (The assumption use to be, xdp_buff->data_hard_start + PAGE_SIZE, but ixgbe+virtio_net broke that assumption). It should actually be fairly easy to implement: * Simply extend xdp_buff with a "data_hard_end" pointer. Now cpumap is more safe... instead of crashing, it can now know/see when it is safe to create an SKB using build_skb (could fallback to dev_alloc_skb). -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer