From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bregans-1.gladserv.net (bregans-1.gladserv.net [185.128.211.58]) (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 C7E0E3A8759; Sat, 4 Jul 2026 11:59:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.128.211.58 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783166362; cv=none; b=ls6lsifEtVnvjIY1sqd+6xwNfvTSjDaqKhN+qMCLSRg9OITUldzoAIls0+UaZ2CFlvC8g2F4kXwzt4SDueO974S9ZfFBmn54nbMbBqJq86v6TpYVbFcHqFGgy8dELBYAqBv4c4FlY0OHvaOCocWOUr5w/g3MTh6Hg944XMgdeAo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783166362; c=relaxed/simple; bh=ZGQ5T5hVMk4bVsB0AhSWuwmKNhetB0SBNETEJC3CzXc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=OLnfFfNZYesde+VJJx+qhw6bhu48P9UzRdBK02js3FSL4HCGfcvaohutBvtHCD6FaRicaJj20ZSBIvUcajJrGcCfVlqvh9y67/PT1GKrsGOZJ1eMBMsYyvS1ESl1JkclQmEkHpxlWjfDiRO3OkYTD/CqS+Y5xGAGHt2/YV2NKfo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=librecast.net; spf=pass smtp.mailfrom=librecast.net; arc=none smtp.client-ip=185.128.211.58 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=librecast.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=librecast.net Date: Sat, 4 Jul 2026 13:58:52 +0200 From: Brett Sheffield To: Simon Schippers Cc: Willem de Bruijn , Jason Wang , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , "Michael S . Tsirkin" , netdev@vger.kernel.org, Simon Horman , Jonathan Corbet , Shuah Khan , Andrew Lunn , Tim Gebauer , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net] tun/tap & vhost-net: make qdisc backpressure opt-in via IFF_BACKPRESSURE Message-ID: References: <20260704112058.95421-1-simon.schippers@tu-dortmund.de> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260704112058.95421-1-simon.schippers@tu-dortmund.de> On 2026-07-04 13:20, Simon Schippers wrote: > Commit 1d6e569b7d0c ("tun/tap & vhost-net: avoid ptr_ring tail-drop > when a qdisc is present") did not show a relevant performance regression > in my testing but on Brett Sheffield's librecast testbed it shows a > significant performance drop. The regression can be pinpointed when > multiple iperf3 TCP threads are sending. For 8 threads the performance > dropped from 13.5 Gbit/s to 9.13 Gbit/s. This is the reason why this > patch makes the qdisc backpressure behavior opt-in. Thanks Simon. I've tested and confirmed this fixes the original failing IPv6 multicast (UDP) test which flagged the problem. Tested-by: Brett A C Sheffield Cheers, Brett -- Brett Sheffield (he/him) Librecast - Decentralising the Internet with Multicast https://librecast.net/ https://blog.brettsheffield.com/