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 50EA8C141; Wed, 24 Sep 2025 05:59:51 +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=1758693596; cv=none; b=BGp0t6Lnl0e3QuEebDkmWXhLEOD+q6+xnDKWL6rD7dvm958Oy17CbS4yLC9UceUr4y8hJP47Z6jj0B5DdqTuxO6ykJKS7nV549/Ysod1zAwGyXvZbY+FjU4q4xm1GR1wSh0XU/JGt7dCFJQK6vme4KVPQbI7yGuYWU9B0+z0Dhs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758693596; c=relaxed/simple; bh=N2MGgVh3FQGohtqhW0fhGVQOd6N06pK4oL5dFsa3MZA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=udhG4LUz1lg8qHNCmcZM5Up7j8LY0XHIj481LUUyxpTTe/BD/fqqvyKkHzPMqw43kC8AiJYU42eneNUeVavlhwHtUQj8IiNfVy3rm1l+qtC/y4J2/uZZKaGHaGLZLjYJkdKv8zxzAXkY1v3GgaxDpUF2tS9RL7BldJ818FNn9XY= 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=W9850TNI; 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="W9850TNI" Received: from [IPV6:2a01:599:c11:dc72:32f8:2997:5bae:168a] (tmo-123-4.customers.d1-online.com [80.187.123.4]) (authenticated bits=0) by unimail.uni-dortmund.de (8.18.1.10/8.18.1.10) with ESMTPSA id 58O5xkO8020717 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Wed, 24 Sep 2025 07:59:47 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=tu-dortmund.de; s=unimail; t=1758693587; bh=N2MGgVh3FQGohtqhW0fhGVQOd6N06pK4oL5dFsa3MZA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=W9850TNIaMIc0VoXTP2OIKP2SMr62bBBkcBJxATnh10lO6SaJrvucmmzYGEH9J1fa WjL92bHKsvKmMhntMlNzps1dqcW4CIOlec4c9Vd8uIITOl+PSJ8+2CWT49N2w8WcLh L1mGHE423T54HZHRSbjqqIDzp3uAkQpx3/CohHYU= Message-ID: <96058e18-bb1e-46d1-99aa-9fdffb965e44@tu-dortmund.de> Date: Wed, 24 Sep 2025 07:59:46 +0200 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 v5 0/8] TUN/TAP & vhost_net: netdev queue flow control to avoid ptr_ring tail drop To: "Michael S. Tsirkin" Cc: willemdebruijn.kernel@gmail.com, jasowang@redhat.com, eperezma@redhat.com, stephen@networkplumber.org, leiyang@redhat.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux.dev, kvm@vger.kernel.org References: <20250922221553.47802-1-simon.schippers@tu-dortmund.de> <20250923105531-mutt-send-email-mst@kernel.org> Content-Language: en-US From: Simon Schippers In-Reply-To: <20250923105531-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 23.09.25 16:55, Michael S. Tsirkin wrote: > On Tue, Sep 23, 2025 at 12:15:45AM +0200, Simon Schippers wrote: >> This patch series deals with TUN, TAP and vhost_net which drop incoming >> SKBs whenever their internal ptr_ring buffer is full. Instead, with this >> patch series, the associated netdev queue is stopped before this happens. >> This allows the connected qdisc to function correctly as reported by [1] >> and improves application-layer performance, see our paper [2]. Meanwhile >> the theoretical performance differs only slightly: >> >> +------------------------+----------+----------+ >> | pktgen benchmarks | Stock | Patched | >> | i5 6300HQ, 20M packets | | | >> +------------------------+----------+----------+ >> | TAP | 2.10Mpps | 1.99Mpps | >> +------------------------+----------+----------+ >> | TAP+vhost_net | 6.05Mpps | 6.14Mpps | >> +------------------------+----------+----------+ >> | Note: Patched had no TX drops at all, | >> | while stock suffered numerous drops. | >> +----------------------------------------------+ >> >> This patch series includes TUN, TAP, and vhost_net because they share >> logic. Adjusting only one of them would break the others. Therefore, the >> patch series is structured as follows: >> 1+2: New ptr_ring helpers for 3 & 4 >> 3: TUN & TAP: Stop netdev queue upon reaching a full ptr_ring > > > so what happens if you only apply patches 1-3? > The netdev queue of vhost_net would be stopped by tun_net_xmit but will never be woken again. >> 4: TUN & TAP: Wake netdev queue after consuming an entry >> 5+6+7: TUN & TAP: ptr_ring wrappers and other helpers to be called by >> vhost_net >> 8: vhost_net: Call the wrappers & helpers >> >> Possible future work: >> - Introduction of Byte Queue Limits as suggested by Stephen Hemminger >> - Adaption of the netdev queue flow control for ipvtap & macvtap >> >> [1] Link: >> https://unix.stackexchange.com/questions/762935/traffic-shaping-ineffective-on-tun-device >> [2] Link: >> https://cni.etit.tu-dortmund.de/storages/cni-etit/r/Research/Publications/2025/Gebauer_2025_VTCFall/Gebauer_VTCFall2025_AuthorsVersion.pdf >> >> Links to previous versions: >> V4: >> https://lore.kernel.org/netdev/20250902080957.47265-1-simon.schippers@tu-dortmund.de/T/#u >> V3: >> https://lore.kernel.org/netdev/20250825211832.84901-1-simon.schippers@tu-dortmund.de/T/#u >> V2: >> https://lore.kernel.org/netdev/20250811220430.14063-1-simon.schippers@tu-dortmund.de/T/#u >> V1: >> https://lore.kernel.org/netdev/20250808153721.261334-1-simon.schippers@tu-dortmund.de/T/#u >> >> Changelog: >> V4 -> V5: >> - Stop the netdev queue prior to producing the final fitting ptr_ring entry >> -> Ensures the consumer has the latest netdev queue state, making it safe >> to wake the queue >> -> Resolves an issue in vhost_net where the netdev queue could remain >> stopped despite being empty >> -> For TUN/TAP, the netdev queue no longer needs to be woken in the >> blocking loop >> -> Introduces new helpers __ptr_ring_full_next and >> __ptr_ring_will_invalidate for this purpose >> >> - vhost_net now uses wrappers of TUN/TAP for ptr_ring consumption rather >> than maintaining its own rx_ring pointer >> >> V3 -> V4: >> - Target net-next instead of net >> - Changed to patch series instead of single patch >> - Changed to new title from old title >> "TUN/TAP: Improving throughput and latency by avoiding SKB drops" >> - Wake netdev queue with new helpers wake_netdev_queue when there is any >> spare capacity in the ptr_ring instead of waiting for it to be empty >> - Use tun_file instead of tun_struct in tun_ring_recv as a more consistent >> logic >> - Use smp_wmb() and smp_rmb() barrier pair, which avoids any packet drops >> that happened rarely before >> - Use safer logic for vhost_net using RCU read locks to access TUN/TAP data >> >> V2 -> V3: Added support for TAP and TAP+vhost_net. >> >> V1 -> V2: Removed NETDEV_TX_BUSY return case in tun_net_xmit and removed >> unnecessary netif_tx_wake_queue in tun_ring_recv. >> >> Thanks, >> Simon :) >> >> Simon Schippers (8): >> __ptr_ring_full_next: Returns if ring will be full after next >> insertion >> Move the decision of invalidation out of __ptr_ring_discard_one >> TUN, TAP & vhost_net: Stop netdev queue before reaching a full >> ptr_ring >> TUN & TAP: Wake netdev queue after consuming an entry >> TUN & TAP: Provide ptr_ring_consume_batched wrappers for vhost_net >> TUN & TAP: Provide ptr_ring_unconsume wrappers for vhost_net >> TUN & TAP: Methods to determine whether file is TUN/TAP for vhost_net >> vhost_net: Replace rx_ring with calls of TUN/TAP wrappers >> >> drivers/net/tap.c | 115 +++++++++++++++++++++++++++++++-- >> drivers/net/tun.c | 136 +++++++++++++++++++++++++++++++++++---- >> drivers/vhost/net.c | 90 +++++++++++++++++--------- >> include/linux/if_tap.h | 15 +++++ >> include/linux/if_tun.h | 18 ++++++ >> include/linux/ptr_ring.h | 54 +++++++++++++--- >> 6 files changed, 367 insertions(+), 61 deletions(-) >> >> -- >> 2.43.0 >