From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 5F6A53B14B1 for ; Tue, 28 Jul 2026 19:22:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785266557; cv=none; b=DzDtIUTgJaeSRSoxSi4rwtghN+oT6nAm/pI7K7nBbbBNPLp/yjqTAfNsklM820Uo19VN6NsE2rj2EAjQEySsUE31Bt2kxjEfDAMOI1GWR26Vk2jqc5S9jizoWFmpZtatvLmACfDCSB3T+kifiTwa9XDraDNZVqdgS27j3ycZ6TE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785266557; c=relaxed/simple; bh=R+zgHjbzWHNJAJSiByZoxeBoJx0H4D0oao8AmHjSzv8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=JtVd/I+eMXXwdLNds+zoJypo4N0hG32LaM1TgbTojv2Dt29QXQUxQRS8tr+z8OlMsfyVrhzR3KrH5id5nxFi6RAOyNTjspZXTw7Ft95M8+xgMVUy28Cqd4V4ZsMC6YZN2yvOA5i/B5tA2kJ/793SrrtapraMm14DTa/T5riziiY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=YUsuxc/L; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b=ZmAYyNef; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="YUsuxc/L"; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b="ZmAYyNef" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1785266554; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=xHDeYJjbxDxQ0a8+BXenwk1PFl2CLayk3cj54C+//40=; b=YUsuxc/LD/Cdb0ir5kKJ7Pd4nJlGSnDsv05SC7+l7XgFcefj/hw5PWgNSsC+1QuOZkJK9N 5aE6F5PkyrQp9UHQ39ImNUdrmuOMf0z7pgYbUW/y3AjBxk5N6mZV1jo7W8XRbMICLJ85Yf l6HrIElmzTA2w2+a2bgYAbAn3UfDYww= Received: from mail-wm1-f71.google.com (mail-wm1-f71.google.com [209.85.128.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-368-xGBY7vA9M2mi0uiOimaDxg-1; Tue, 28 Jul 2026 15:22:33 -0400 X-MC-Unique: xGBY7vA9M2mi0uiOimaDxg-1 X-Mimecast-MFC-AGG-ID: xGBY7vA9M2mi0uiOimaDxg_1785266552 Received: by mail-wm1-f71.google.com with SMTP id 5b1f17b1804b1-496b408a5c0so980805e9.0 for ; Tue, 28 Jul 2026 12:22:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=google; t=1785266552; x=1785871352; darn=vger.kernel.org; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:from:to:cc:subject :date:message-id:reply-to:content-type; bh=xHDeYJjbxDxQ0a8+BXenwk1PFl2CLayk3cj54C+//40=; b=ZmAYyNef6hfH1A29wQ0a3rJG3AqRb/61mozxJpJVo/TVou6pvJbQJKqcIPcdt8j5FW CC0DSndAMIjtNXxpKrzAdL8qj6E5P5390pQbEsmcwm+9Sda1XGVDiOnGU+1oyPtzIHUY F4legdo1V9LYUqG0/SEoQ7XN4+HO4f6M+LmOydoPXegqQxLRrDj+I9ZJlt/mgQ/wc/MW OzEjHtFAWGkCDSEjj2s7Z1It0zMTZozeLLurDqpnPtTdeSoK6QrI3O4iNLUvre4OSEa7 nWce7RBt+Ka+P/5YfYfsMcLLzCDcjB++ZQr6nNRC9j5jHUzqwsyI5tjPVDRzjGoM8ox5 FEMA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1785266552; x=1785871352; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=xHDeYJjbxDxQ0a8+BXenwk1PFl2CLayk3cj54C+//40=; b=WFSX4TggSgcEWEw0X4/w+74zosLJ2tkgJCv3+j9Mclhg8uUMuKQzlpJMEas5m6JANX yPo9srhSv/7PzMxXO2vCk4e+3Nes2RNcBTyGXFINyxaWPGwH6DXLZZk7r3TDilg08Syp 8TIrSgnFcw9YPE0h8cif5S0hSjxmAvSaguYx/lafwFKAPE4CR7n1W+MT4vxjqnYr+vZ6 6XMT97eji/7isrm2PMkftxNOQrTMkCqBKaZBQFrPbZIRx55bVjoJJJW60J9EBzh7A2IH AtTJxWpRADYU66HKvAjXCf5iaP+bmw2bdeCcPkGXCiqrszenFmCvWe7/aGenQbV142D1 ci5A== X-Forwarded-Encrypted: i=1; AHgh+Rp3GBFHjBUejhqtQQd2p5pyT7dgyThKc0pTKcWzLp/nf1bkrZFLZ3a/VYwJLyLEjmu/Ed4BKdt1+NAgOSY=@vger.kernel.org X-Gm-Message-State: AOJu0YzTF64uXcCRN/3HBraLwNnw3b7VL49q+YFmElZ4XVZV0i8Gzf63 gDmVKpI2gF8plVkTgGy4Xd3MK9ryyCjfOsbenwDLk5J8ag6+1yzO/1QX2VrVRoWC4k2qmuJxdXx FGeduOr+NrtEAK5T4oa+zMYzGWSvUw/IeF+5yv0YbzlAnVX8RYOBq16nYUdVwBWludw== X-Gm-Gg: AR+sD12d+8Xh8pPJKgxXc3LYXH60uoOsZzMZ1SkfyZHQzy53+7SuU/NJRqhTc56W37f wg2eMWjiTxpwX8kL+0m0d0UDpoTmfCWtXefX7tTrq6xpMmCgCEdq5rVVqTbcCcjdKP36ST/QGs6 HsgA7KS5silOH6OxSP6+DPQ1ikUf+4dDsqErMrdpn4+0/4C8oThaHNdWdJn48EQ/hTXTN0vOlOg +q7B2SAG0GEz1X5V3fOAsmEuUiqmWGzvAOC6Ve/oADvYEpeA22KKljzY4vDvp+AE0sWxC9c3HVc i9COO9+28jTZk9BFRKiZq+I2YsbaZgryOYE0s1VXPbxU1HZfe38yvYMSxywkDadbPtHPlnAq3Nv 9mq6R9VFnd5Ko9b6XYy6qz38= X-Received: by 2002:a05:600c:1c1a:b0:495:5fdf:2075 with SMTP id 5b1f17b1804b1-496c60c1c4dmr38408205e9.0.1785266551636; Tue, 28 Jul 2026 12:22:31 -0700 (PDT) X-Received: by 2002:a05:600c:1c1a:b0:495:5fdf:2075 with SMTP id 5b1f17b1804b1-496c60c1c4dmr38407915e9.0.1785266551088; Tue, 28 Jul 2026 12:22:31 -0700 (PDT) Received: from redhat.com (ppp-94-66-118-61.home.otenet.gr. [94.66.118.61]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-496c44afaecsm112946795e9.2.2026.07.28.12.22.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 Jul 2026 12:22:30 -0700 (PDT) Date: Tue, 28 Jul 2026 15:22:26 -0400 From: "Michael S. Tsirkin" To: Simon Schippers Cc: netdev@vger.kernel.org, Willem de Bruijn , Jason Wang , Andrew Lunn , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Eugenio =?iso-8859-1?Q?P=E9rez?= , Simon Horman , Tim Gebauer , Brett Sheffield , kvm@vger.kernel.org, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH net 0/4] Revert "tun/tap & vhost-net: apply qdisc backpressure on full ptr_ring to reduce TX drops" Message-ID: <20260728152204-mutt-send-email-mst@kernel.org> References: <20260728092240.250257-1-simon.schippers@tu-dortmund.de> Precedence: bulk X-Mailing-List: linux-kernel@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: <20260728092240.250257-1-simon.schippers@tu-dortmund.de> On Tue, Jul 28, 2026 at 11:22:36AM +0200, 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 causes a > significant throughput drop in an IPv6 multicast testcase. The regression > can be pinpointed to multiple iperf3 TCP threads sending: for 8 threads > the throughput dropped from 13.5 Gbit/s to 9.13 Gbit/s. > > Therefore this series reverts the qdisc backpressure work. > > Making the backpressure opt-in via a new IFF_BACKPRESSURE flag was > proposed in [1], but a new IFF_* flag needs more review scrutiny than is > available at the moment, so a revert was requested instead. The opt-in > will be resubmitted for net-next later. Acked-by: Michael S. Tsirkin Thanks! > [1] Link: https://lore.kernel.org/netdev/20260709095511.168235-1-simon.schippers@tu-dortmund.de/ > > Reported-by: Brett Sheffield > Closes: https://lore.kernel.org/netdev/akVnoOYQOrt8k-Gu@karahi.librecast.net/ > > Simon Schippers (4): > Revert "tun/tap & vhost-net: avoid ptr_ring tail-drop when a qdisc is > present" > Revert "ptr_ring: move free-space check into separate helper" > Revert "vhost-net: wake queue of tun/tap after ptr_ring consume" > Revert "tun/tap: add ptr_ring consume helper with netdev queue wakeup" > > drivers/net/tun.c | 109 +++------------------------------------ > drivers/vhost/net.c | 21 +++----- > include/linux/if_tun.h | 3 -- > include/linux/ptr_ring.h | 20 +------ > 4 files changed, 14 insertions(+), 139 deletions(-) > > > base-commit: b14361aca6350ff7907b0e9903c7b94dc7d5d4a0 > -- > 2.43.0