From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BCC98C433B4 for ; Mon, 12 Apr 2021 10:45:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9467D61352 for ; Mon, 12 Apr 2021 10:45:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239635AbhDLKpi (ORCPT ); Mon, 12 Apr 2021 06:45:38 -0400 Received: from mail.kernel.org ([198.145.29.99]:49558 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239062AbhDLKph (ORCPT ); Mon, 12 Apr 2021 06:45:37 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 374F36134F; Mon, 12 Apr 2021 10:45:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1618224319; bh=/yFjMUiGPFNWMalqJeYQqR6ZQK8rTlZ0JOYyZI10Zdc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=uZy2CKXyxIM6LSMKsoGOrwjzJ/dzK4T3EygMvD1b5iY/Y9IS6+Iws23AYOEqSIrj6 OdpJPAmBiJdx7juSCPSIRT56CER2Da7apU5bnf2PxfAHx9gY1c0uUPdOpivELFu2Mg eOOyS9JYEFqX0MDAtR5HdMr2QM1flv+b/ucccMOc= Date: Mon, 12 Apr 2021 12:45:16 +0200 From: Greg Kroah-Hartman To: "Michael S. Tsirkin" Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org, Xuan Zhuo , Eric Dumazet , Jason Wang , virtualization@lists.linux-foundation.org, "David S. Miller" Subject: Re: [PATCH 5.10 055/188] virtio_net: Do not pull payload in skb->head Message-ID: References: <20210412084013.643370347@linuxfoundation.org> <20210412084015.479443671@linuxfoundation.org> <20210412051010-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210412051010-mutt-send-email-mst@kernel.org> Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Mon, Apr 12, 2021 at 05:11:40AM -0400, Michael S. Tsirkin wrote: > On Mon, Apr 12, 2021 at 10:39:29AM +0200, Greg Kroah-Hartman wrote: > > From: Eric Dumazet > > > > commit 0f6925b3e8da0dbbb52447ca8a8b42b371aac7db upstream. > > > > Xuan Zhuo reported that commit 3226b158e67c ("net: avoid 32 x truesize > > under-estimation for tiny skbs") brought a ~10% performance drop. > > > > The reason for the performance drop was that GRO was forced > > to chain sk_buff (using skb_shinfo(skb)->frag_list), which > > uses more memory but also cause packet consumers to go over > > a lot of overhead handling all the tiny skbs. > > > > It turns out that virtio_net page_to_skb() has a wrong strategy : > > It allocates skbs with GOOD_COPY_LEN (128) bytes in skb->head, then > > copies 128 bytes from the page, before feeding the packet to GRO stack. > > > > This was suboptimal before commit 3226b158e67c ("net: avoid 32 x truesize > > under-estimation for tiny skbs") because GRO was using 2 frags per MSS, > > meaning we were not packing MSS with 100% efficiency. > > > > Fix is to pull only the ethernet header in page_to_skb() > > > > Then, we change virtio_net_hdr_to_skb() to pull the missing > > headers, instead of assuming they were already pulled by callers. > > > > This fixes the performance regression, but could also allow virtio_net > > to accept packets with more than 128bytes of headers. > > > > Many thanks to Xuan Zhuo for his report, and his tests/help. > > > > Fixes: 3226b158e67c ("net: avoid 32 x truesize under-estimation for tiny skbs") > > Reported-by: Xuan Zhuo > > Link: https://www.spinics.net/lists/netdev/msg731397.html > > Co-Developed-by: Xuan Zhuo > > Signed-off-by: Xuan Zhuo > > Signed-off-by: Eric Dumazet > > Cc: "Michael S. Tsirkin" > > Cc: Jason Wang > > Cc: virtualization@lists.linux-foundation.org > > Acked-by: Jason Wang > > Signed-off-by: David S. Miller > > Signed-off-by: Greg Kroah-Hartman > > > > Note that an issue related to this patch was recently reported. > It's quite possible that the root cause is a bug elsewhere > in the kernel, but it probably makes sense to defer the backport > until we know more ... Thanks, I'll go drop it from all 4 queues. If you all find out that all is good, and it should be added back, please let us at stable@vger know about it. thanks, greg k-h