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 E7840C433FE for ; Wed, 16 Nov 2022 10:35:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233230AbiKPKfA (ORCPT ); Wed, 16 Nov 2022 05:35:00 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38912 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233199AbiKPKcl (ORCPT ); Wed, 16 Nov 2022 05:32:41 -0500 Received: from violet.fr.zoreil.com (violet.fr.zoreil.com [IPv6:2001:4b98:dc0:41:216:3eff:fe56:8398]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6234B6550; Wed, 16 Nov 2022 02:28:28 -0800 (PST) Received: from violet.fr.zoreil.com ([127.0.0.1]) by violet.fr.zoreil.com (8.17.1/8.17.1) with ESMTP id 2AGARw6D892604; Wed, 16 Nov 2022 11:27:58 +0100 DKIM-Filter: OpenDKIM Filter v2.11.0 violet.fr.zoreil.com 2AGARw6D892604 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fr.zoreil.com; s=v20220413; t=1668594479; bh=4EJYbote49QLZzbD6v8Bx/T1+B6bUVPK/0OQXhufnCI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=eL6p3lCVw2j4oqUlhIGY8quZMF3jef02Xb3qL92MylAFpQV1tg3FfXLMVRiSIanrh WIOEY4ihjo80RbGE4yc5kXHL2FtFmTc1WLVkigbenxdMUXXNa/8bweUTODaO5c6iRd tJPbHbzNIoYwfCgUM3sS7brzqHT3heRZDPSoRMQ8= Received: (from romieu@localhost) by violet.fr.zoreil.com (8.17.1/8.17.1/Submit) id 2AGARwbP892603; Wed, 16 Nov 2022 11:27:58 +0100 Date: Wed, 16 Nov 2022 11:27:58 +0100 From: Francois Romieu To: Zhang Changzhong Cc: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, mdf@kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net v2 3/3] net: nixge: fix tx queue handling Message-ID: References: <1668525024-38409-1-git-send-email-zhangchangzhong@huawei.com> <1668525024-38409-4-git-send-email-zhangchangzhong@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Organisation: Land of Sunshine Inc. Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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); } -- Ueimor