From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lj1-x244.google.com (mail-lj1-x244.google.com [IPv6:2a00:1450:4864:20::244]) (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 CDA313B29E for ; Tue, 23 Jun 2020 11:21:57 -0400 (EDT) Received: by mail-lj1-x244.google.com with SMTP id q19so23927328lji.2 for ; Tue, 23 Jun 2020 08:21:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=tr37O5uIjbbDZDAW0ms8mx/DAZjqwSvJvQcl7csuSN0=; b=byl3fJw5UyZ0rFdSS+Um9wdt7vdW2CetCx2ND7w6YNn2N/9G8YiW3kDAZPihyMEjBA ZpfTKqQJPZP1mASqoUlrLhH5x+b2PhhVGa5m8SB//epel55/fqHq4ykfxoSv+cg2zOsQ iKRD6PReMX+KqVw/koz5Pv+hpdwS554jvE4kfrWqGN5Nq7o6+q0qIXy19qQomjIeYL3r s5L6AXYO7b+Ukwwa5/rI1Ka73HS/f5JB/kzwcCwaIWYPCSE0cq0BJ4r5BcBl9vojsH1i NU1XkXRmUA6xl0CTVOebE+AQdgFMIEK8PtSr6rhx59GnfchnUBF6j8QgSKAlzqyNln4J MB3w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=tr37O5uIjbbDZDAW0ms8mx/DAZjqwSvJvQcl7csuSN0=; b=ILle4NtwhI+thNM4yUofqwy69PYdodcIa+t2fCd1PN3NzT1/OiCrbAi0DCfCXuIZdQ wOh+G+2LsjuTvdWLEnVkE63MD4hdszANeubzTTt09i3QL2/2B4XFanjL907m6k4XBfmH DBdUSSulluie32Pa1aU1rpB7WESq6y63OvZlG49wnvUe9Z6J0q/jUUwME2FFtw+lDDg5 KisZOIIpsJ+inNNGG0Iy5OgSSbG+ckCtJ3q7uSoLpscXgvKRO5hujbCEIH6REEn/TXpu ithpdBW7pGdPpjuguIrAQkWF4r3DguPTFMRBZ5dZWMzu1rkr5ERiOQWKc/te3U2QsuRb q6lA== X-Gm-Message-State: AOAM5323h1j8ootTN1u885zntSVFGxd2PxaUOhz4afX3lPTJMkLPpKn0 zf7i85BrXn0HTCmXo3vdurY= X-Google-Smtp-Source: ABdhPJxu9foJbx15154ksP0Chm89NSDX6AAJ4cU5twIS3eHQ69/smmOQEJ957nU2peflNQqd4AB6NQ== X-Received: by 2002:a2e:6c12:: with SMTP id h18mr12259814ljc.62.1592925716575; Tue, 23 Jun 2020 08:21:56 -0700 (PDT) Received: from jonathartonsmbp.lan (83-245-237-85-nat-p.elisa-mobile.fi. [83.245.237.85]) by smtp.gmail.com with ESMTPSA id l22sm3365885ljg.41.2020.06.23.08.21.55 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Tue, 23 Jun 2020 08:21:55 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 11.5 \(3445.9.5\)) From: Jonathan Morton In-Reply-To: <87lfkdrgip.fsf@toke.dk> Date: Tue, 23 Jun 2020 18:21:54 +0300 Cc: Jose Blanquicet , cake@lists.bufferbloat.net, marco maniezzo Content-Transfer-Encoding: quoted-printable Message-Id: <8959B7A6-0B20-4812-BC9D-812DD4F3BCC4@gmail.com> References: <877dvzt84w.fsf@toke.dk> <87lfkdrgip.fsf@toke.dk> To: =?utf-8?Q?Toke_H=C3=B8iland-J=C3=B8rgensen?= X-Mailer: Apple Mail (2.3445.9.5) Subject: Re: [Cake] [CAKE] Rate is much lower than expected - CPU load is higher than expected 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: Tue, 23 Jun 2020 15:21:58 -0000 > On 23 Jun, 2020, at 5:41 pm, Toke H=C3=B8iland-J=C3=B8rgensen = wrote: >=20 > Right, well if you're not running out of CPU I guess it could be a > timing issue. The CAKE shaper relies on accurate timestamps and the > qdisc watchdog timer to schedule the transmission of packets. A loaded > system can simply miss deadlines, which would be consistent with the > behaviour you're seeing. >=20 > In fact, when looking into this a bit more, I came across this commit > that seemed to observe the same behaviour in sch_fq: > https://git.kernel.org/torvalds/c/fefa569a9d4b >=20 > So I guess we could try to do something similar in CAKE. Actually, we already do. The first version of Cake's shaper was based = closely on the one in sch_fq at the time, and I modified it after = noticing that it had a very limited maximum throughput when timer = resolution was poor (eg. at 1kHz on an old PC without HPET hardware, we = could only get 1k pps). Now, any late timer event will result in a = burst being issued to catch up with the proper schedule. The only time = that wouldn't work is if the queue is empty. If the patches currently being trialled are not sufficient, then perhaps = we could try something counter-intuitive: switch on "flows" instead of = "flowblind", and enable the ack-filter. That should result in fewer = small packets to process, as the ack-filter will coalesce some acks, = especially under load. It might also help to select "satellite" AQM = parameters, reducing the amount of processing needed at that layer. - Jonathan Morton