From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi1-x234.google.com (mail-oi1-x234.google.com [IPv6:2607:f8b0:4864:20::234]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 32B173B29E for ; Wed, 19 Feb 2020 08:52:33 -0500 (EST) Received: by mail-oi1-x234.google.com with SMTP id a22so23810297oid.13 for ; Wed, 19 Feb 2020 05:52:33 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=wT2Mz3VZvDSBN4+AqFgbIFYATb8JgE9hJEnzrv4C6hc=; b=bzt9Bv7S5ZieIkInqfzmAv2GOQe6kBbEDgsRRSpyyjUPDdTpqJPun7Eaf1speg+LGG G1nKDuzHIX6r6W+/U5wP5OktD2RV4NBzOfsl10h9O1mXtvePFHt9+iTJP0OqwyxtUUuw KcpFod+IrDC/1jCPo0J+miVJs/VFkGOxC18XFHMuTJJH6Gy6GeBrBaiopvoxaJCgbNaV hexbLOhrlzBFp1zEmIxb8a+seSuRVDiva6RerrrLnFXN8nKGll6KQpZNz+0B/Cq+ivlF yvenrXcbpN0lBXJ/IUOvvrf9KrBwp5eqZBvlKGrCZNEPxW1t+U3Pldnml7JsHUgeGviL xYHQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=wT2Mz3VZvDSBN4+AqFgbIFYATb8JgE9hJEnzrv4C6hc=; b=jbkQC3ZLVW3xKIRShgQtwvsWKchL25ovfb/fGtEJeLzgbWxVlPw+opOXddVfK52hvg Jq6rgN4YM4YL+/l0LrZKIabWF6Hm6JkLqy1J88SUiPlIuA5lT0sBZvdHxqLvAvQIiipT tY+KlEBMrRU8X9tqVkddt/GaUZNc7ZGEcX4QrLh5trgBwbe5efWbuVmO1Du3/jIVQALw Jlz46lmC+hDY4G6mgONjWHxljulmXkiH8Pb+YtZQby1XkNYDxPQgC97aZILi4UIJeuLR ZvrPB/nGlwE7cf3MskpPI3MjDCb3Ih+gZMwomFjw3y628nxxUIUMKxIImrt5/1trShr7 hpeg== X-Gm-Message-State: APjAAAWH0yOtKpZ24cb8++AGXYzF56UkxgdbzG/SXA2y4o59447kq3dr N5i0cCZ5RsRNvP3fIwwyoPBbSRB3W+RVPi0Xof5o+w== X-Google-Smtp-Source: APXvYqwN0N9lI9B7PfB7965sK9ADcvQlPWJZKXrVhFMluQRyCWqTcAZCruesINs34ZSubBbxQcXev5WD2UMCw2rpGSw= X-Received: by 2002:a05:6808:64e:: with SMTP id z14mr4417337oih.79.1582120352257; Wed, 19 Feb 2020 05:52:32 -0800 (PST) MIME-Version: 1.0 References: <9dfa6edf-0b7a-981a-e980-1187e461f6eb@GMail.com> In-Reply-To: <9dfa6edf-0b7a-981a-e980-1187e461f6eb@GMail.com> From: Neal Cardwell Date: Wed, 19 Feb 2020 08:52:16 -0500 Message-ID: To: Alexey Ivanov Cc: bloat Content-Type: text/plain; charset="UTF-8" Subject: Re: [Bloat] Excessive throttling with fq X-BeenThere: bloat@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: General list for discussing Bufferbloat List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 19 Feb 2020 13:52:33 -0000 On Wed, Feb 19, 2020 at 1:58 AM Alexey Ivanov wrote: > > FWIW, we recently noticed a similar issue with our CUBIC senders after > we've enabled FQ on them (4.15 kernel.) > > Disabling train detection in hystart did fix the problem: > > # echo 2 > /sys/module/tcp_cubic/parameters/hystart_detect > > [1] > https://github.com/torvalds/linux/blob/master/net/ipv4/tcp_cubic.c#L76-L77 Yes, Hystart was not designed to work with pacing, so when fq is used Hystart ACK train detection needs to be disabled. Eric Dumazet made some recent fixes (Linux v5.6) to make Hystart dynamically adapt to the presence of pacing to avoid this issue: 473900a504e5 tcp_cubic: optimize hystart_update() 35821fc2b41c tcp_cubic: remove one conditional from hystart_update() cff04e2da308 tcp_cubic: switch bictcp_clock() to usec resolution 42f3a8aaae66 tcp_cubic: tweak Hystart detection for short RTT flows ede656e84658 tcp_cubic: make Hystart aware of pacing f278b99ca6b2 tcp_cubic: refactor code to perform a divide only when needed neal