From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-il1-x133.google.com (mail-il1-x133.google.com [IPv6:2607:f8b0:4864:20::133]) (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 417923B29E for ; Sat, 4 Dec 2021 20:25:08 -0500 (EST) Received: by mail-il1-x133.google.com with SMTP id j21so6646669ila.5 for ; Sat, 04 Dec 2021 17:25:08 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=MMGMYWewILDmeTAqITv/cnd2HN5oltggpb0LJVo+RIU=; b=QGFYibftLRelQMupTolP27/qRbwkHwAoKBe+bH9qa5R5xJ49ZHgrNQt03DQXlfQ9iE KCdJipk+mGscPvoLs6vlffa65GTHMV+VxA8wE82qJ35fCHCD/TX63LNkDjvlzePcHj02 pU7LQC2xjn+T0Bc44RKjVejcXBH0lBvs8vDYpGi7aTAE3rM+j4DyPigXnuVg9hfgRWeb 1Sc67XfhGZ90huX+PTYCPgQ9P8QiQmn5TupqbFZbXG0A7+p673u8cWSJqOw1XHA9pNwO i0uhj6JPt22jYnhjW9aGdJ/o9eSh9N1n5CgcSP5Hacch4Zsz6ICDkoiKRaK8Wbp9Xs+G 75sg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=MMGMYWewILDmeTAqITv/cnd2HN5oltggpb0LJVo+RIU=; b=m9JvhbSjzG1FsNZEOtJG0zkpZR0dfFBid9D18valijhRGw+9Pd/rkU3pJWz4qyjJME pEeNpChZVksOCcSGGfm7pKvN36EoQwd1gi2xPiGrZGGkJlm7UJQJV2F9C3KQCvXzrAGW yy2E6JZEtcdfKEJ6ynb3LDlm0U2MB97XMLcv9K9PDytd90z8uAAVmC3PRNNFXyHOJMZu tVhKTwgCGEeJvBSjJjUAIGlGTrQorl/nj+jILsl/S9GAxhQe2zBt2gi63N/36xJrfMo8 NzxjMBtELQbF4VV17866FgkoxoZ9v5k3vLJKO1jIq6T4UnpEcWVjyt+S2GJ9h4Ea4Fae 9aNg== X-Gm-Message-State: AOAM532kOPi9wEBA31mfZwH8sux0nMpodQ75067mgACjl/pDtr3rI9mX xefn9ENLZ5HkgnOqutMeuUlvFjAyWRrUOJa35dY= X-Google-Smtp-Source: ABdhPJzhQzKAxzGcc9bh5TsRpSLO9+sdYSKwDaRH9X4KHT6SYloEC3xGVTAOCzeLIFxo70GALg8SN3nTEvpCf3XTlmE= X-Received: by 2002:a05:6e02:20ea:: with SMTP id q10mr23221041ilv.283.1638667507528; Sat, 04 Dec 2021 17:25:07 -0800 (PST) MIME-Version: 1.0 References: <0A6AB0B7-E010-42E3-BAEE-FCBFA5995117@gmail.com> <1638658910.996417608@apps.rackspace.com> In-Reply-To: <1638658910.996417608@apps.rackspace.com> From: Dave Taht Date: Sat, 4 Dec 2021 17:24:55 -0800 Message-ID: To: "David P. Reed" Cc: Jonathan Morton , jonathan.kua@deakin.edu.au, Cake List Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Subject: Re: [Cake] Understanding the Achieved Rate Multiplication Effect in FlowQueue-based AQM Bottleneck X-BeenThere: cake@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: Cake - FQ_codel the next generation List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 05 Dec 2021 01:25:08 -0000 I too have been trying to get below 1ms (heck, 3ms) precision or at least, resolution. I came up with the most promising thing I can think of for interactions in a multithreaded environment yet, I think. glibc has long mapped the kernel clock page into process memory, so i was thinking (hoping) that mmaping that on top of itself a zillion times and using that as my test data source for writes out across the network I'd get some really fine grained insights. Haven't got around to it yet. On Sat, Dec 4, 2021 at 3:01 PM David P. Reed wrote: > > I agree with your broad assessment, Jonathan. > > > > The self-interference problem within a host isn't just a network problem.= It's a user-space scheduler problem as well. > > > > There are lots of interactions between user-space scheduler (in the case = of Linux, the "Completely Fair Scheduler" and its quantum, which is set by = the HZ variable at boot) and the network stack in the kernel. This interact= ions have non-trivial effects when mutliple flows are independently created= by concurrent processes). > > > > Lately, I've been studying, for reasons related to my day job, the comple= x interactions of timing at sub-millisecond scale among threads and process= es on a single system in Linux. I/O driven by threads become highly correla= ted, and so assuming "independence" among flow timing is just not a good a= ssumption. > > > > The paper observes the results of "dependencies" that couple/resonate. > > > > On Friday, December 3, 2021 7:09pm, "Jonathan Morton" said: > > > > On 4 Dec, 2021, at 12:27 am, Dave Taht wrote: > > > > > > > > https://jonathankua.github.io/preprints/jkua-ieeelcn2021_understanding_= ar_preprint-20jul2021.pdf > > > > > > I would love it if somehow the measured effects of chunklets against = cake's > > per-host/per flow fq was examined one day. > > > > I haven't actually measured it, but based on what the above paper says,= I can make > > some firm predictions: > > > > 1: When competing against traffic to the same local host, the performan= ce effects > > they describe will be present. > > > > 2: When competing against traffic to a different local-network host, th= e > > performance effects they describe will be attenuated or even entirely a= bsent. > > > > 3: They noted one or two cases of observable effects of hash collisions= in their > > tests with FQ-Codel. These will be greatly reduced in prevalence with C= ake, due > > to the set-associative hash function which specifically addresses that = phenomenon. > > > > - Jonathan Morton > > _______________________________________________ > > Cake mailing list > > Cake@lists.bufferbloat.net > > https://lists.bufferbloat.net/listinfo/cake > > --=20 I tried to build a better future, a few times: https://wayforward.archive.org/?site=3Dhttps%3A%2F%2Fwww.icei.org Dave T=C3=A4ht CEO, TekLibre, LLC