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 3A2B7C4332F for ; Wed, 16 Nov 2022 12:00:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233575AbiKPMAr (ORCPT ); Wed, 16 Nov 2022 07:00:47 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46768 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232367AbiKPMAX (ORCPT ); Wed, 16 Nov 2022 07:00:23 -0500 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D9E9C1181E; Wed, 16 Nov 2022 03:52:37 -0800 (PST) Received: from dggpeml500022.china.huawei.com (unknown [172.30.72.54]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4NC1Xc21q1zqSMs; Wed, 16 Nov 2022 19:48:48 +0800 (CST) Received: from dggpeml500006.china.huawei.com (7.185.36.76) by dggpeml500022.china.huawei.com (7.185.36.66) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Wed, 16 Nov 2022 19:52:36 +0800 Received: from [10.174.178.240] (10.174.178.240) by dggpeml500006.china.huawei.com (7.185.36.76) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Wed, 16 Nov 2022 19:52:35 +0800 Subject: Re: [PATCH net v2 3/3] net: nixge: fix tx queue handling To: Francois Romieu CC: , , , , , , References: <1668525024-38409-1-git-send-email-zhangchangzhong@huawei.com> <1668525024-38409-4-git-send-email-zhangchangzhong@huawei.com> From: Zhang Changzhong Message-ID: <01c16617-aaf0-3a2e-1498-a9a75ae242af@huawei.com> Date: Wed, 16 Nov 2022 19:52:34 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.178.240] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To dggpeml500006.china.huawei.com (7.185.36.76) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/11/16 18:27, Francois Romieu wrote: > Zhang Changzhong : >> On 2022/11/16 7:04, Francois Romieu wrote: >>> Zhang Changzhong : > [...] >>>> diff --git a/drivers/net/ethernet/ni/nixge.c b/drivers/net/ethernet/ni/nixge.c >>>> index 91b7ebc..3776a03 100644 >>>> --- a/drivers/net/ethernet/ni/nixge.c >>>> +++ b/drivers/net/ethernet/ni/nixge.c >>> [...] >>>> static netdev_tx_t nixge_start_xmit(struct sk_buff *skb, >>>> @@ -518,10 +523,15 @@ static netdev_tx_t nixge_start_xmit(struct sk_buff *skb, >>>> cur_p = &priv->tx_bd_v[priv->tx_bd_tail]; >>>> tx_skb = &priv->tx_skb[priv->tx_bd_tail]; >>>> >>>> - if (nixge_check_tx_bd_space(priv, num_frag + 1)) { >>>> - if (!netif_queue_stopped(ndev)) >>>> - netif_stop_queue(ndev); >>>> - return NETDEV_TX_OK; >>>> + if (unlikely(nixge_check_tx_bd_space(priv, num_frag + 1))) { >>>> + /* Should not happen as last start_xmit call should have >>>> + * checked for sufficient space and queue should only be >>>> + * woken when sufficient space is available. >>>> + */ >>> >>> Almost. IRQ triggering after nixge_start_xmit::netif_stop_queue and >>> before nixge_start_xmit::smp_mb may wrongly wake queue. >>> >> >> I don't know what you mean by "wronly wake queue". The queue is woken >> only when there is sufficient for next packet. > > Between nixge_start_xmit::netif_stop_queue and nixge_start_xmit::smp_mb, > "next" packet is current packet in hard_start_xmit. However said current > packet may not be accounted for in the IRQ context transmit completion > handler. > > [nixge_start_xmit] > > ++priv->tx_bd_tail; > priv->tx_bd_tail %= TX_BD_NUM; > > /* Stop queue if next transmit may not have space */ > if (nixge_check_tx_bd_space(priv, MAX_SKB_FRAGS + 1)) { > netif_stop_queue(ndev); > > Which value does [nixge_start_xmit_done] read as priv->tx_bd_tail at > this point ? The value set a few lines above or some older value ? > > /* Matches barrier in nixge_start_xmit_done */ > smp_mb(); > > /* Space might have just been freed - check again */ > if (!nixge_check_tx_bd_space(priv, MAX_SKB_FRAGS + 1)) > netif_wake_queue(ndev); > } > Got it! Thanks a lot for your detailed explanation. Best Regards, Changzhong