From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7D06A171AE for ; Mon, 8 May 2023 10:30:22 +0000 (UTC) Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BAE9E24AA6 for ; Mon, 8 May 2023 03:30:16 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1683541815; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=xPsu5YVFrEenCLv+iZuaZj4Zmadv4HGEz/gE1xJGp6I=; b=X2vU80jWY9jzUI70O4wx9R8c/moYJ/2Npe/Dv8xKTHg9dqNLWUpeR3j3xthbZhWlCEql0j //TH9Zy1TJDrGHQ7CtLXYeWHehK3Ap+tLCAim/M790I9Bd1bK0tyFLwK0bFfzNf8sR6yHm 7REo+jykB0qtEdbd543M2Bcc6mxQizs= Received: from mail-wr1-f71.google.com (mail-wr1-f71.google.com [209.85.221.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-492-6E3ftKzmOl-Xy_-BaZ-o7w-1; Mon, 08 May 2023 06:30:14 -0400 X-MC-Unique: 6E3ftKzmOl-Xy_-BaZ-o7w-1 Received: by mail-wr1-f71.google.com with SMTP id ffacd0b85a97d-302cdf5d034so2695659f8f.0 for ; Mon, 08 May 2023 03:30:14 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1683541813; x=1686133813; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=xPsu5YVFrEenCLv+iZuaZj4Zmadv4HGEz/gE1xJGp6I=; b=e8wMBooGRZoZiXke+d3A1KGZxLALMlLGE6OU0WGu7isrH/8H+IfpiwdiPaaDs4PN3w 3H8Rvw6w3KgZmY1bLiOWcjmkykqzmDS+nWHHeehnm7TaTRjPlybdbJ+AZeKsINV2OYXp 4Dz7MQrOhAcVNIQqgrPKgd91DU62G8RLIP/cIgivpRBuj0526RNNXmTn27URZvLC1r/w XGMRiQqR5U7URpVJmF3NCXAjlnXqnoKA5wZqIr9zlg/E5WL0fd/y1GzYWrxDZKoI0ELE 8U+A4u3HYxA0dFX/i1twijLHAJnIS+XD8fsJjELqyg176bzOQUEI+8Qk1p58dzam4Ldg ascw== X-Gm-Message-State: AC+VfDxEDLWld4AlK0E23DBrYnA6drEV2dbH5pOLhKJvBZzwiINJZgKz /rF5M7FZL8+RYkZSBOHVnXZbQc/fPEXsZG9aTY7VvYjGK0ziXadYlC70J4KnPEYBqngkDAtxUhw 7BajJrneaHNhscET6 X-Received: by 2002:adf:e943:0:b0:306:2cf5:79dc with SMTP id m3-20020adfe943000000b003062cf579dcmr7718611wrn.35.1683541813556; Mon, 08 May 2023 03:30:13 -0700 (PDT) X-Google-Smtp-Source: ACHHUZ7ykEugQ/sjlWtVtf+RWhyd+Wdn5biO6WeKJ/H0kdlQUIkECfX6aLaJNv/UFBtqbWwQjfrirw== X-Received: by 2002:adf:e943:0:b0:306:2cf5:79dc with SMTP id m3-20020adfe943000000b003062cf579dcmr7718591wrn.35.1683541813164; Mon, 08 May 2023 03:30:13 -0700 (PDT) Received: from redhat.com ([31.187.78.15]) by smtp.gmail.com with ESMTPSA id h14-20020a5d6e0e000000b0030631dcbea6sm10959097wrz.77.2023.05.08.03.30.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 08 May 2023 03:30:12 -0700 (PDT) Date: Mon, 8 May 2023 06:30:07 -0400 From: "Michael S. Tsirkin" To: Xuan Zhuo Cc: huangml@yusur.tech, zy@yusur.tech, Jason Wang , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , "open list:VIRTIO CORE AND NET DRIVERS" , "open list:NETWORKING DRIVERS" , open list , Hao Chen , hengqi@linux.alibaba.com Subject: Re: [PATCH] virtio_net: set default mtu to 1500 when 'Device maximum MTU' bigger than 1500 Message-ID: <20230508062928-mutt-send-email-mst@kernel.org> References: <20230506021529.396812-1-chenh@yusur.tech> <1683341417.0965195-4-xuanzhuo@linux.alibaba.com> <07b6b325-9a15-222f-e618-d149b57cbac2@yusur.tech> <20230507045627-mutt-send-email-mst@kernel.org> <1683511319.099806-2-xuanzhuo@linux.alibaba.com> <20230508020953-mutt-send-email-mst@kernel.org> <1683526688.7492425-1-xuanzhuo@linux.alibaba.com> <20230508024147-mutt-send-email-mst@kernel.org> <1683531716.238961-1-xuanzhuo@linux.alibaba.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1683531716.238961-1-xuanzhuo@linux.alibaba.com> X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net On Mon, May 08, 2023 at 03:41:56PM +0800, Xuan Zhuo wrote: > On Mon, 8 May 2023 02:43:24 -0400, "Michael S. Tsirkin" wrote: > > On Mon, May 08, 2023 at 02:18:08PM +0800, Xuan Zhuo wrote: > > > On Mon, 8 May 2023 02:15:46 -0400, "Michael S. Tsirkin" wrote: > > > > On Mon, May 08, 2023 at 10:01:59AM +0800, Xuan Zhuo wrote: > > > > > On Sun, 7 May 2023 04:58:58 -0400, "Michael S. Tsirkin" wrote: > > > > > > On Sat, May 06, 2023 at 04:56:35PM +0800, Hao Chen wrote: > > > > > > > > > > > > > > > > > > > > > 在 2023/5/6 10:50, Xuan Zhuo 写道: > > > > > > > > On Sat, 6 May 2023 10:15:29 +0800, Hao Chen wrote: > > > > > > > > > When VIRTIO_NET_F_MTU(3) Device maximum MTU reporting is supported. > > > > > > > > > If offered by the device, device advises driver about the value of its > > > > > > > > > maximum MTU. If negotiated, the driver uses mtu as the maximum > > > > > > > > > MTU value. But there the driver also uses it as default mtu, > > > > > > > > > some devices may have a maximum MTU greater than 1500, this may > > > > > > > > > cause some large packages to be discarded, > > > > > > > > > > > > > > > > You mean tx packet? > > > > > > > Yes. > > > > > > > > > > > > > > > > If yes, I do not think this is the problem of driver. > > > > > > > > > > > > > > > > Maybe you should give more details about the discard. > > > > > > > > > > > > > > > In the current code, if the maximum MTU supported by the virtio net hardware > > > > > > > is 9000, the default MTU of the virtio net driver will also be set to 9000. > > > > > > > When sending packets through "ping -s 5000", if the peer router does not > > > > > > > support negotiating a path MTU through ICMP packets, the packets will be > > > > > > > discarded. If the peer router supports negotiating path mtu through ICMP > > > > > > > packets, the host side will perform packet sharding processing based on the > > > > > > > negotiated path mtu, which is generally within 1500. > > > > > > > This is not a bugfix patch, I think setting the default mtu to within 1500 > > > > > > > would be more suitable here.Thanks. > > > > > > > > > > > > I don't think VIRTIO_NET_F_MTU is appropriate for support for jumbo packets. > > > > > > The spec says: > > > > > > The device MUST forward transmitted packets of up to mtu (plus low level ethernet header length) size with > > > > > > gso_type NONE or ECN, and do so without fragmentation, after VIRTIO_NET_F_MTU has been success- > > > > > > fully negotiated. > > > > > > VIRTIO_NET_F_MTU has been designed for all kind of tunneling devices, > > > > > > and this is why we set mtu to max by default. > > > > > > > > > > > > For things like jumbo frames where MTU might or might not be available, > > > > > > a new feature would be more appropriate. > > > > > > > > > > > > > > > So for jumbo frame, what is the problem? > > > > > > > > > > We are trying to do this. @Heng > > > > > > > > > > Thanks. > > > > > > > > It is not a problem as such. But VIRTIO_NET_F_MTU will set the > > > > default MTU not just the maximum one, because spec seems to > > > > say it can. > > > > > > I see. > > > > > > In the case of Jumbo Frame, we also hope that the driver will set the default > > > directly to the max mtu. Just like what you said "Bigger packets = better > > > performance." > > > > > > I don't know, in any scenario, when the hardware supports a large mtu, but we do > > > not want the user to use it by default. > > > > When other devices on the same LAN have mtu set to 1500 and > > won't accept bigger packets. > > So, that depends on pmtu/tcp-probe-mtu. > > If the os without pmtu/tcp-probe-mtu has a bigger mtu, then it's big packet > will lost. > > Thanks. > pmtu is designed for routing. LAN is supposed to be configured with a consistent MTU. > > > > > Of course, the scene that this patch > > > wants to handle does exist, but I have never thought that this is a problem at > > > the driver level. > > > > > > Thanks. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > so I changed the MTU to a more > > > > > > > > > general 1500 when 'Device maximum MTU' bigger than 1500. > > > > > > > > > > > > > > > > > > Signed-off-by: Hao Chen > > > > > > > > > --- > > > > > > > > > drivers/net/virtio_net.c | 5 ++++- > > > > > > > > > 1 file changed, 4 insertions(+), 1 deletion(-) > > > > > > > > > > > > > > > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > > > > > > > > index 8d8038538fc4..e71c7d1b5f29 100644 > > > > > > > > > --- a/drivers/net/virtio_net.c > > > > > > > > > +++ b/drivers/net/virtio_net.c > > > > > > > > > @@ -4040,7 +4040,10 @@ static int virtnet_probe(struct virtio_device *vdev) > > > > > > > > > goto free; > > > > > > > > > } > > > > > > > > > > > > > > > > > > - dev->mtu = mtu; > > > > > > > > > + if (mtu > 1500) > > > > > > > > > > > > > > > > s/1500/ETH_DATA_LEN/ > > > > > > > > > > > > > > > > Thanks. > > > > > > > > > > > > > > > > > + dev->mtu = 1500; > > > > > > > > > + else > > > > > > > > > + dev->mtu = mtu; > > > > > > > > > dev->max_mtu = mtu; > > > > > > > > > } > > > > > > > > > > > > > > > > > > -- > > > > > > > > > 2.27.0 > > > > > > > > > > > > > > > > > > > > >