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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 00C4EC433FE for ; Thu, 25 Nov 2021 07:30:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234815AbhKYHd7 (ORCPT ); Thu, 25 Nov 2021 02:33:59 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:41112 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235352AbhKYHb5 (ORCPT ); Thu, 25 Nov 2021 02:31:57 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1637825326; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=KAYyix8FJ3fNIZWmvJGEU4BGlkJhgJqUuDlAboJ19Kw=; b=cjGAQ7X3lJTjnQMAMPPC0uMAVZk9Oeh0Lw3QfRNXywxgyLksNtXIrNz+Y4NQ/Nvhp5zbMg /yED+1ea/d8oS6aJE04vAHITpK/0iyFivmHd2RXRWJ5CP7jcmV1PH4RRlkAnAPHDv3BpH/ kVdEil/4JkG6ETnqCm6gRUPpakwtsds= Received: from mail-lf1-f71.google.com (mail-lf1-f71.google.com [209.85.167.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-120-w-U1ysq3PhSncByxcmVWMw-1; Thu, 25 Nov 2021 02:28:44 -0500 X-MC-Unique: w-U1ysq3PhSncByxcmVWMw-1 Received: by mail-lf1-f71.google.com with SMTP id h40-20020a0565123ca800b00402514d959fso2791088lfv.7 for ; Wed, 24 Nov 2021 23:28:44 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=KAYyix8FJ3fNIZWmvJGEU4BGlkJhgJqUuDlAboJ19Kw=; b=EZktB2X1UbmJUsL6zx84h+PvgiO5EX5aunlbSFFCRjA8qwvC6s5tPwQj2b+6XWGn5q 9/YwueU6Fptqc194Eib+NlGvK0jwyl6VJQNloZ9UK6w2pU/X+WUbignn5o1b31BV1TP/ BXPA9REIUEoR8wmkLXQIVbtwDoDVZ7RMHk+GzPpyEQb9C6NtkwFQJCaShur2gZ51lmnv yJLlQZuwn2KfPby8bDPPtjwtBAPSr/Q4bK4OPRjgCGBnhOS4rGYdGtxRqiwY/Oeom7Ju qCjLAi6NYTlDLbgJ4sBjq/Ym4U3WMjhZ7JhtfpSpeYqrlQmgd8uA5Z/6fj600EXBcsxC mHzQ== X-Gm-Message-State: AOAM533WvTWgR8KChLsRUIhQ2aQsiaZLKKlhWJ3aBz9cMafXqmC8mER/ 12F7+HauICl6IzPGPwoGFlnX75nSCGymREOVgQosXH3eX5jLcbjNjhU2L+97K7jQpG9C8nezx+K 05H9Cs1hW+jedC+SwM1aI86Hm1qS0JgU4gaNpA3w/ X-Received: by 2002:ac2:5310:: with SMTP id c16mr22375077lfh.580.1637825323077; Wed, 24 Nov 2021 23:28:43 -0800 (PST) X-Google-Smtp-Source: ABdhPJwR0Oj+HYVWJiKnMqDcsVDTqq/srl4I6uPRZ9iNPuv2p0Bkt1dEPXaslgNkp/hh9kpZ3ybmiGxzpKXdjayduxU= X-Received: by 2002:ac2:5310:: with SMTP id c16mr22375068lfh.580.1637825322885; Wed, 24 Nov 2021 23:28:42 -0800 (PST) MIME-Version: 1.0 References: <20211125060547.11961-1-jasowang@redhat.com> <20211125015532-mutt-send-email-mst@kernel.org> <20211125021308-mutt-send-email-mst@kernel.org> <20211125022442-mutt-send-email-mst@kernel.org> In-Reply-To: <20211125022442-mutt-send-email-mst@kernel.org> From: Jason Wang Date: Thu, 25 Nov 2021 15:28:31 +0800 Message-ID: Subject: Re: [PATCH net] virtio-net: enable big mode correctly To: "Michael S. Tsirkin" Cc: virtualization , netdev , linux-kernel , Eli Cohen Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 25, 2021 at 3:26 PM Michael S. Tsirkin wrote: > > On Thu, Nov 25, 2021 at 03:20:07PM +0800, Jason Wang wrote: > > On Thu, Nov 25, 2021 at 3:15 PM Michael S. Tsirkin wrote: > > > > > > On Thu, Nov 25, 2021 at 03:11:58PM +0800, Jason Wang wrote: > > > > On Thu, Nov 25, 2021 at 3:00 PM Michael S. Tsirkin wrote: > > > > > > > > > > On Thu, Nov 25, 2021 at 02:05:47PM +0800, Jason Wang wrote: > > > > > > When VIRTIO_NET_F_MTU feature is not negotiated, we assume a very > > > > > > large max_mtu. In this case, using small packet mode is not correct > > > > > > since it may breaks the networking when MTU is grater than > > > > > > ETH_DATA_LEN. > > > > > > > > > > > > To have a quick fix, simply enable the big packet mode when > > > > > > VIRTIO_NET_F_MTU is not negotiated. > > > > > > > > > > This will slow down dpdk hosts which disable mergeable buffers > > > > > and send standard MTU sized packets. > > > > > > > > > > > We can do optimization on top. > > > > > > > > > > I don't think it works like this, increasing mtu > > > > > from guest >4k never worked, > > > > > > > > Looking at add_recvbuf_small() it's actually GOOD_PACKET_LEN if I was not wrong. > > > > > > OK, even more so then. > > > > > > > > we can't regress everyone's > > > > > performance with a promise to maybe sometime bring it back. > > > > > > > > So consider it never work before I wonder if we can assume a 1500 as > > > > max_mtu value instead of simply using MAX_MTU? > > > > > > > > Thanks > > > > > > You want to block guests from setting MTU to a value >GOOD_PACKET_LEN? > > > > Yes, or fix the issue to let large packets on RX work (e.g as the TODO > > said, size the buffer: for <=4K mtu continue to work as > > add_recvbuf_small(), for >= 4K switch to use big). > > Right. The difficulty is with changing modes, current code isn't > designed for it. I think it might work if we reset the device during the mode change. Thanks > > > > Maybe ... it will prevent sending large packets which did work ... > > > > Yes, but it's strange to allow TX but not RX > > > > > I'd tread carefully here, and I don't think this kind of thing is net > > > material. > > > > I agree consider it can't be fixed easily. > > > > Thanks > > > > > > > > > > > > > > > > Reported-by: Eli Cohen > > > > > > Cc: Eli Cohen > > > > > > Signed-off-by: Jason Wang > > > > > > > > > > > > --- > > > > > > drivers/net/virtio_net.c | 7 ++++--- > > > > > > 1 file changed, 4 insertions(+), 3 deletions(-) > > > > > > > > > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > > > > > index 7c43bfc1ce44..83ae3ef5eb11 100644 > > > > > > --- a/drivers/net/virtio_net.c > > > > > > +++ b/drivers/net/virtio_net.c > > > > > > @@ -3200,11 +3200,12 @@ static int virtnet_probe(struct virtio_device *vdev) > > > > > > dev->mtu = mtu; > > > > > > dev->max_mtu = mtu; > > > > > > > > > > > > - /* TODO: size buffers correctly in this case. */ > > > > > > - if (dev->mtu > ETH_DATA_LEN) > > > > > > - vi->big_packets = true; > > > > > > } > > > > > > > > > > > > + /* TODO: size buffers correctly in this case. */ > > > > > > + if (dev->max_mtu > ETH_DATA_LEN) > > > > > > + vi->big_packets = true; > > > > > > + > > > > > > if (vi->any_header_sg) > > > > > > dev->needed_headroom = vi->hdr_len; > > > > > > > > > > > > -- > > > > > > 2.25.1 > > > > > > > > >