From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.toke.dk (mail.toke.dk [45.145.95.4]) (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 2E8621DC9B1 for ; Tue, 19 Aug 2025 08:51:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.145.95.4 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755593510; cv=none; b=CeyKrSk88yriyuMm+XPMZSkWBoUylLeZ5KE3Mhfv/H4wsYbakeMK7DbTpXvzgT6xA7FBNOPrT2L1zx7hwACtWn6UaGmsw/TDtIXt7s/Be7yLEUTXF/EtAY+pGIi/ab/99asWzBU5yXfVQb/NJsBlSiz+oJtiLEQpKg4oh1KPHBk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755593510; c=relaxed/simple; bh=jgcAdVqxyFY4tD8DGpZ73j1dA0dSsUrPS79OJAYl0NY=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=MobuUCzqgBmxyfaQP7W7OyPshARfXLNsopnm2GuqUideUAetZjW2v2YP9Z8y++T2aQ0eZ4u597r5wO2PjNhe3u2IIOcqZbYLL0QKjU7FYXzoF2tbYLfjpllwPu1clsNGa/M0ZZxSLnl6X4PebKjhOk4iJL1tdUrCMpXOanbK2Sc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=toke.dk; spf=pass smtp.mailfrom=toke.dk; dkim=pass (2048-bit key) header.d=toke.dk header.i=@toke.dk header.b=BUMIAagK; arc=none smtp.client-ip=45.145.95.4 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=toke.dk Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=toke.dk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=toke.dk header.i=@toke.dk header.b="BUMIAagK" From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=toke.dk; s=20161023; t=1755593500; bh=jgcAdVqxyFY4tD8DGpZ73j1dA0dSsUrPS79OJAYl0NY=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=BUMIAagKBvzWPsGJjIyM4bF6MsPKG8CuWrTP3PR/VzeuxXMCacozumt0jFWQ9kvu0 iILiri72jmnCaISAYIM6NK9ID0yjfsroRs/dJu57L1t+PEEsL6dm+4PTerw+1lLHJy HzwsxTExfT1Jq174m0ZNg6heNhXnXAZvMYOR2xcMJRVgRfYISTvuKlsljTQRGJWnFd jins3iFTYF/MUD9DTZqO/C/CfGLEgwaZehXlnvNvlyFgFpasn7cE4kFjkBGTAcivUX R6yaTXq3YfPwtDnCuv3Vd98JDcbRZPVzefuNdY3zZAgR6/v6rrzH8ZDVUtkGZ3GGfV E0ZTg6UmeKCzA== To: William Liu , netdev@vger.kernel.org Cc: dave.taht@gmail.com, jhs@mojatatu.com, xiyou.wangcong@gmail.com, pabeni@redhat.com, kuba@kernel.org, savy@syst3mfailure.io, jiri@resnulli.us, davem@davemloft.net, edumazet@google.com, horms@kernel.org, cake@lists.bufferbloat.net, William Liu Subject: Re: [PATCH net v2 1/2] net/sched: Make cake_enqueue return NET_XMIT_CN when past buffer_limit In-Reply-To: <20250819033601.579821-1-will@willsroot.io> References: <20250819033601.579821-1-will@willsroot.io> Date: Tue, 19 Aug 2025 10:51:33 +0200 X-Clacks-Overhead: GNU Terry Pratchett Message-ID: <871pp7k82y.fsf@toke.dk> 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-Transfer-Encoding: quoted-printable William Liu writes: > The following setup can trigger a WARNING in htb_activate due to > the condition: !cl->leaf.q->q.qlen > > tc qdisc del dev lo root > tc qdisc add dev lo root handle 1: htb default 1 > tc class add dev lo parent 1: classid 1:1 \ > htb rate 64bit > tc qdisc add dev lo parent 1:1 handle f: \ > cake memlimit 1b > ping -I lo -f -c1 -s64 -W0.001 127.0.0.1 > > This is because the low memlimit leads to a low buffer_limit, which > causes packet dropping. However, cake_enqueue still returns > NET_XMIT_SUCCESS, causing htb_enqueue to call htb_activate with an > empty child qdisc. We should return NET_XMIT_CN when packets are > dropped from the same tin and flow. > > I do not believe return value of NET_XMIT_CN is necessary for packet > drops in the case of ack filtering, as that is meant to optimize > performance, not to signal congestion. > > Fixes: 046f6fd5daef ("sched: Add Common Applications Kept Enhanced (cake)= qdisc") > Signed-off-by: William Liu > Reviewed-by: Savino Dicanosa Acked-by: Toke H=C3=B8iland-J=C3=B8rgensen