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 D3B8DC678D5 for ; Wed, 8 Mar 2023 12:24:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231426AbjCHMYH (ORCPT ); Wed, 8 Mar 2023 07:24:07 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42300 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231464AbjCHMXs (ORCPT ); Wed, 8 Mar 2023 07:23:48 -0500 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 49393BF8F0 for ; Wed, 8 Mar 2023 04:22:34 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1678278074; 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=FYUSGl+c2i/XrGfwxUOIC1FfAmTL8/NIk2jsBnOFyek=; b=dNXslAKaVVzoJaoP6flqaB/MeRyrz4fIAyVMB9vj+Yr96c67tZv4yno51oV8/5wBeKYBcd 6N+HwcgyvGnWP/oKoUykoRYkeuxg0G67PAAh6soIBTajTqODsuokgzQHtt3hGOn5Y/zdwE SyhMH+w52z+tXSv+5BrcSqWmByTevcc= Received: from mail-ed1-f69.google.com (mail-ed1-f69.google.com [209.85.208.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-434-VsEGj9QJPUimkPCWz4MEZw-1; Wed, 08 Mar 2023 07:21:13 -0500 X-MC-Unique: VsEGj9QJPUimkPCWz4MEZw-1 Received: by mail-ed1-f69.google.com with SMTP id b1-20020aa7dc01000000b004ad062fee5eso23353591edu.17 for ; Wed, 08 Mar 2023 04:21:13 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1678278072; h=in-reply-to: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=FYUSGl+c2i/XrGfwxUOIC1FfAmTL8/NIk2jsBnOFyek=; b=hmi0v9QmYZcPNmPE58yNOu/zlP0iV9SM8rqaSbbNzJ+q83cInD/VpajQIharwGXoeG OtjdgXaTA0aLGcRfPdW2+ecuBX2LDW/GimWEcca9bFA7NqT1IoENl6Rohafq02EKxUs/ 0czATkrtQan4ZCzX4gjzutdrMLsURRB1vSIw8JAy+QmzzDRQbWh7QOCeCk6jaNw2myou wDtItMJeNJiQ/5mBkBQv/ruPyy7vd+GiMT+hQN3jY/kbozmbiO44PwW616UX/52tM/CP +8PSYMD/uL0x2ufAN867UJIb7JdnJrDF4Fp7chmf+ER8zDE49h55YIWPVTyyrpnjii8z OyIA== X-Gm-Message-State: AO0yUKXuQNLhSViHxdqSSWj2KpNnguKmnkiGFVghTGqzOhadoLev+wEF 1VKQNMII7Mw2SzHT17QLdd4basMIRcyeqpRWePjbEK5YoHYqJNo+ydGJMSgNExpyPIrBPxjubuF UfgK353KX566eRcBp X-Received: by 2002:aa7:d856:0:b0:4af:6e95:861b with SMTP id f22-20020aa7d856000000b004af6e95861bmr23390138eds.2.1678278072619; Wed, 08 Mar 2023 04:21:12 -0800 (PST) X-Google-Smtp-Source: AK7set+6tZBfhWzjylNGTyxDwu7Yy+PpamZXGOVNIhYLZOhQ3DZ5QD/rfxx44WLOJiGYe6hsxp2zJQ== X-Received: by 2002:aa7:d856:0:b0:4af:6e95:861b with SMTP id f22-20020aa7d856000000b004af6e95861bmr23390108eds.2.1678278072292; Wed, 08 Mar 2023 04:21:12 -0800 (PST) Received: from redhat.com ([2.52.138.216]) by smtp.gmail.com with ESMTPSA id r15-20020a50c00f000000b004bbc90e1fa3sm8087835edb.93.2023.03.08.04.21.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Mar 2023 04:21:11 -0800 (PST) Date: Wed, 8 Mar 2023 07:21:07 -0500 From: "Michael S. Tsirkin" To: Yunsheng Lin Cc: Xuan Zhuo , Jason Wang , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , virtualization@lists.linux-foundation.org, bpf@vger.kernel.org, Yichun Zhang , Alexander Duyck , netdev@vger.kernel.org Subject: Re: [PATCH net, stable v1 3/3] virtio_net: add checking sq is full inside xdp xmit Message-ID: <20230308071921-mutt-send-email-mst@kernel.org> References: <20230308024935.91686-1-xuanzhuo@linux.alibaba.com> <20230308024935.91686-4-xuanzhuo@linux.alibaba.com> <7eea924e-5cc3-8584-af95-04587f303f8f@huawei.com> <1678259647.118581-1-xuanzhuo@linux.alibaba.com> <5a4564dc-af93-4305-49a4-5ca16d737bc3@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5a4564dc-af93-4305-49a4-5ca16d737bc3@huawei.com> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Wed, Mar 08, 2023 at 04:13:12PM +0800, Yunsheng Lin wrote: > On 2023/3/8 15:14, Xuan Zhuo wrote: > > On Wed, 8 Mar 2023 14:59:36 +0800, Yunsheng Lin wrote: > >> On 2023/3/8 10:49, Xuan Zhuo wrote: > >>> If the queue of xdp xmit is not an independent queue, then when the xdp > >>> xmit used all the desc, the xmit from the __dev_queue_xmit() may encounter > >>> the following error. > >>> > >>> net ens4: Unexpected TXQ (0) queue failure: -28 > >>> > >>> This patch adds a check whether sq is full in xdp xmit. > >>> > >>> Fixes: 56434a01b12e ("virtio_net: add XDP_TX support") > >>> Reported-by: Yichun Zhang > >>> Signed-off-by: Xuan Zhuo > >>> Reviewed-by: Alexander Duyck > >>> Acked-by: Michael S. Tsirkin > >>> --- > >>> drivers/net/virtio_net.c | 3 +++ > >>> 1 file changed, 3 insertions(+) > >>> > >>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > >>> index 46bbddaadb0d..1a309cfb4976 100644 > >>> --- a/drivers/net/virtio_net.c > >>> +++ b/drivers/net/virtio_net.c > >>> @@ -767,6 +767,9 @@ static int virtnet_xdp_xmit(struct net_device *dev, > >>> } > >>> ret = nxmit; > >>> > >>> + if (!is_xdp_raw_buffer_queue(vi, sq - vi->sq)) > >>> + check_sq_full_and_disable(vi, dev, sq); > >>> + > >> > >> Sorry if I missed something obvious here. > >> > >> As the comment in start_xmit(), the current skb is added to the sq->vq, so > >> NETDEV_TX_BUSY can not be returned. > >> > >> /* If running out of space, stop queue to avoid getting packets that we > >> * are then unable to transmit. > >> * An alternative would be to force queuing layer to requeue the skb by > >> * returning NETDEV_TX_BUSY. However, NETDEV_TX_BUSY should not be > >> * returned in a normal path of operation: it means that driver is not > >> * maintaining the TX queue stop/start state properly, and causes > >> * the stack to do a non-trivial amount of useless work. > >> * Since most packets only take 1 or 2 ring slots, stopping the queue > >> * early means 16 slots are typically wasted. > >> */ > >> > >> It there any reason not to check the sq->vq->num_free at the begin of start_xmit(), > >> if the space is not enough for the current skb, TX queue is stopped and NETDEV_TX_BUSY > >> is return to the stack to requeue the current skb. > >> > >> It seems it is the pattern that most network driver follow, and it seems we can avoid > >> calling check_sq_full_and_disable() in this patch and not wasting 16 slots as mentioned > >> in the comment above. > >> > > > > > > > > * netdev_tx_t (*ndo_start_xmit)(struct sk_buff *skb, > > * struct net_device *dev); > > * Called when a packet needs to be transmitted. > > * Returns NETDEV_TX_OK. Can return NETDEV_TX_BUSY, but you should stop > > * the queue before that can happen; it's for obsolete devices and weird > > * corner cases, but the stack really does a non-trivial amount > > * of useless work if you return NETDEV_TX_BUSY. > > * Required; cannot be NULL. > > Thanks for the pointer. It is intersting, it seems most driver is not flollowing > the suggestion. Yes - I don't know why. > I found out why the above comment was added, but I am not sure I understand > what does "non-trivial amount of useless work" means yet. > https://lists.linuxfoundation.org/pipermail/virtualization/2015-April/029718.html dev_requeue_skb -- MST