From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from unimail.uni-dortmund.de (mx1.hrz.uni-dortmund.de [129.217.128.51]) (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 927BB31AF3F; Wed, 26 Nov 2025 09:24:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=129.217.128.51 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764149094; cv=none; b=esB7ZJUjR7WOdw9EMa/nbA5wExMWcePemP8oQaupAilnSjiIJMx1igk4+GcHt1+1bIWe+wYGsfJCEzmfGdqGly+8szPTMSaeqPEN0J+4bWorN31KyOZqHSEN2bx1voFafaaiSZP9mBQ3kS8p6vnQJGCS5DG9AWpukGHLSvix724= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764149094; c=relaxed/simple; bh=7VTWCzte1EfKGKmLVq1yaZwVoVRWDe1aGMmitEojN7M=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=iSuAmQqKSz/XaRgMit++efXmM5lXFhJiLtHUvV7PVObERIrL1g1RApIlnWDnLaJrP8E+ClOgud+XAkzUnylIVEUQ/NOm9/164ajZhqRqAdKi1sJsfAMan2z8YqyI0bHZ4jI7BHqxAHlo+p/Eq5DZB7YCI0rfTFqeIDloQsfQprM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=tu-dortmund.de; spf=pass smtp.mailfrom=tu-dortmund.de; dkim=pass (1024-bit key) header.d=tu-dortmund.de header.i=@tu-dortmund.de header.b=aASOKI8k; arc=none smtp.client-ip=129.217.128.51 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=tu-dortmund.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=tu-dortmund.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=tu-dortmund.de header.i=@tu-dortmund.de header.b="aASOKI8k" Received: from [129.217.186.248] ([129.217.186.248]) (authenticated bits=0) by unimail.uni-dortmund.de (8.18.1.10/8.18.1.10) with ESMTPSA id 5AQ9OhSB003998 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Wed, 26 Nov 2025 10:24:43 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=tu-dortmund.de; s=unimail; t=1764149083; bh=7VTWCzte1EfKGKmLVq1yaZwVoVRWDe1aGMmitEojN7M=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=aASOKI8kUL2H9I+qMmTsEud3+WUWpK7Ir9IKspC1KOdkD/FxWUsqCPamTD7SILa49 fnM//TGAQXNPKrxiq0bVC+jEtyGWnyBH4VBwSajHO6ovInJklAVuA/S+jSl8IlG1jN A96YYepdNeyqsGuhzmo9EbHHG9sb5LsVdN5SogDM= Message-ID: <2bc56d3e-f4da-41d5-ab63-29c63525eb30@tu-dortmund.de> Date: Wed, 26 Nov 2025 10:24:42 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: [PATCH net-next v6 0/8] tun/tap & vhost-net: netdev queue flow control to avoid ptr_ring tail drop To: "Michael S. Tsirkin" Cc: Jason Wang , willemdebruijn.kernel@gmail.com, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, eperezma@redhat.com, jon@nutanix.com, tim.gebauer@tu-dortmund.de, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux.dev References: <20251120152914.1127975-1-simon.schippers@tu-dortmund.de> <20251126021327-mutt-send-email-mst@kernel.org> Content-Language: en-US From: Simon Schippers In-Reply-To: <20251126021327-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 11/26/25 08:15, Michael S. Tsirkin wrote: > On Fri, Nov 21, 2025 at 10:22:54AM +0100, Simon Schippers wrote: >> I agree, but I really would like to reduce the buffer bloat caused by the >> default 500 TUN / 1000 TAP packet queue without losing performance. > > that default is part of the userspace API and can't be changed. > just change whatever userspace is creating your device. > Yes, but I’m thinking about introducing a new interface flag like IFF_BQL. However, as noted earlier, there are significant implementation challenges. I think there can be advantages to something like VPN's on mobile devices where the throughput varies between a few Mbit/s (small TUN/TAP queue is fine) and multiple Gbit/s (need a bigger queue).