From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 BB4C920E003; Tue, 15 Apr 2025 15:43:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744731808; cv=none; b=Nhk12nXV1LuyiPl31+rNeTDM7QvenOBqsgTJ3BXuU6hGyDef0qCfkGQeArXXcZKgYLLjpPk+3j7cLUf8qBQ+c27g6hj/VLZqcDAaIFSB1aKVAakjtJfk/iYssdqio+T2HVwCG7QuT9LsHUJDCgmKi/DPrwnWgl4n1TgdiIAljXo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744731808; c=relaxed/simple; bh=ccucVTibC96ZiE4Hr+vlu4U/HFUEw1R8eJ/1QIq1PMQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=elEZ0qfqdlfXCt02D6F/5gNyYObDy9kWUG4qnjzsoSchVzHHj/vYIXwlQ2aj0b8c1Ilu5zHIGUoS1Oj77TcyFllzxxzf6cRbqU/hIKkUf7pSHeauYFntYdXldA4SL4Wv83VDFaVtCOVVhsBL61xsPWrRDJeGRqb4EIi8vgQ8cOI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ifTFX7Ua; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ifTFX7Ua" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2A4B8C4CEEB; Tue, 15 Apr 2025 15:43:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1744731808; bh=ccucVTibC96ZiE4Hr+vlu4U/HFUEw1R8eJ/1QIq1PMQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=ifTFX7Ua7Nbn0m/QP8+nFy/VLJx29jtfQVfAth5qMaRqnLiKKiVhnU7p2Z2PovKQo uChH/Esdx8AnHOV3oQ4/4geGq/LY74Y5FmXH2gGpkmhushoEeFh5xReUjl1JFbyQld syxlCD2xV3YT8wp8aKBwOFZDKCo2L68q4PNPsdlAzBO8Yk9AzTHcMZ0JtzeTdxwp8K RDju9zjvaGHhktQ7BwU44t5hBezPXGhC/K831x0jH/wk4a+dSK54dr5xPcd7/dxKzC rkDUNEiWtewS8loLsWu0iGFgdYGCCC8Aa85w7j2huxFBmv4tO26xCpK8tG1U77jTYZ RqiwlFKmxyy/A== Message-ID: Date: Tue, 15 Apr 2025 08:43:27 -0700 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next V4 1/2] net: sched: generalize check for no-queue qdisc on TX queue Content-Language: en-US To: Jesper Dangaard Brouer , netdev@vger.kernel.org, Jakub Kicinski Cc: bpf@vger.kernel.org, tom@herbertland.com, Eric Dumazet , "David S. Miller" , Paolo Abeni , =?UTF-8?Q?Toke_H=C3=B8iland-J=C3=B8rgensen?= , makita.toshiaki@lab.ntt.co.jp, kernel-team@cloudflare.com, phil@nwl.cc References: <174472463778.274639.12670590457453196991.stgit@firesoul> <174472469906.274639.14909448343817900822.stgit@firesoul> From: David Ahern In-Reply-To: <174472469906.274639.14909448343817900822.stgit@firesoul> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/15/25 7:44 AM, Jesper Dangaard Brouer wrote: > The "noqueue" qdisc can either be directly attached, or get default > attached if net_device priv_flags has IFF_NO_QUEUE. In both cases, the > allocated Qdisc structure gets it's enqueue function pointer reset to > NULL by noqueue_init() via noqueue_qdisc_ops. > > This is a common case for software virtual net_devices. For these devices > with no-queue, the transmission path in __dev_queue_xmit() will bypass > the qdisc layer. Directly invoking device drivers ndo_start_xmit (via > dev_hard_start_xmit). In this mode the device driver is not allowed to > ask for packets to be queued (either via returning NETDEV_TX_BUSY or > stopping the TXQ). > > The simplest and most reliable way to identify this no-queue case is by > checking if enqueue == NULL. > > The vrf driver currently open-codes this check (!qdisc->enqueue). While > functionally correct, this low-level detail is better encapsulated in a > dedicated helper for clarity and long-term maintainability. > > To make this behavior more explicit and reusable, this patch introduce a > new helper: qdisc_txq_has_no_queue(). Helper will also be used by the > veth driver in the next patch, which introduces optional qdisc-based > backpressure. > > This is a non-functional change. > > Signed-off-by: Jesper Dangaard Brouer > --- > drivers/net/vrf.c | 4 +--- > include/net/sch_generic.h | 8 ++++++++ > 2 files changed, 9 insertions(+), 3 deletions(-) > > /* Local traffic destined to local address. Reinsert the packet to rx > diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h > index d48c657191cd..b6c177f7141c 100644 > --- a/include/net/sch_generic.h > +++ b/include/net/sch_generic.h > @@ -803,6 +803,14 @@ static inline bool qdisc_tx_changing(const struct net_device *dev) > return false; > } > > +/* "noqueue" qdisc identified by not having any enqueue, see noqueue_init() */ > +static inline bool qdisc_txq_has_no_queue(const struct netdev_queue *txq) > +{ > + struct Qdisc *qdisc = rcu_access_pointer(txq->qdisc); > + > + return qdisc->enqueue == NULL; Did checkpatch not complain that this should be '!qdisc->enqueue' ? Reviewed-by: David Ahern