From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-x22c.google.com (mail-pg0-x22c.google.com [IPv6:2607:f8b0:400e:c05::22c]) (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 63FF43B2A2 for ; Mon, 5 Dec 2016 12:10:07 -0500 (EST) Received: by mail-pg0-x22c.google.com with SMTP id p66so138653198pga.2 for ; Mon, 05 Dec 2016 09:10:07 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=networkplumber-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=XzpA+4ciI4YWlqsw+vJVzJMwbF2w4y1ZF/PHVJ6Nlm4=; b=1DU9ZeT9FM3HXErU8uA/W8EzJXqYtvavrlLpTMlsflRjcFjSR8krxJsWuaTUGVyZAh VqaTb/akqoerSKXb2YtGASeQtSQqWIK3mjhiOT39M+AHNJnNQtO+EL+59pQGzD8c2uFA YP/5fSsfC2lBDAOT12Uh0UEiJxCvEp3M8WeXYQ8ApyCxp0WfdRJtCAtKbGqtA6eBNO5t 9yJd1J6lPqD4PPJrRHWAEKLuDITmYRlTl/peyo1Zf3M9FHTE+SujokmOPdFPxYBnXGy1 jkjObruXq2bjyWRqB9xY4MNcCpUa0Txy/yg7tnvqiQKs7FZ0lWs2TSGFizHRE4RZXB20 g4XA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:cc:subject:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=XzpA+4ciI4YWlqsw+vJVzJMwbF2w4y1ZF/PHVJ6Nlm4=; b=g8pGxaconarsOtbDSLwv/OClMXqREmKHxtlXD5cXj6JZLPhKD2G+UVBoxXZlWhCIJ3 nyqVyvsd8cgTsB6hRnrPBKXSpPHSgsgyXdjxEnnqA1EpUcf/2Fnz+jg+x1H9QmLXNTBn 5UzCIeS/NjVB3Ng89TVIp45pMAHXAxz8cv3i251Wy2f3I7AlP8BWQn5JJyRv/HpKK7NW PNnmDaZ8xsXXn2L3qEi/J3aEHcru4KLlMN1sNz0dhHIwjs3QXPm/yDyV6b0uZ0pH3qX/ VaB1p76gT+YuBwdvnslYZyAsttrbwK10+jtBdqACT72VK+YRuifkp1o8/K7zSwaMq9M5 URng== X-Gm-Message-State: AKaTC00M0XH4zBxpxCmmsJ54DkjUj2/WGG+favsAU2QRGs1mznkSgoGbVgiNIJub5q1Nzw== X-Received: by 10.99.124.20 with SMTP id x20mr70026722pgc.142.1480957806577; Mon, 05 Dec 2016 09:10:06 -0800 (PST) Received: from xeon-e3 (204-195-18-65.wavecable.com. [204.195.18.65]) by smtp.gmail.com with ESMTPSA id q145sm28821145pfq.22.2016.12.05.09.10.06 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 05 Dec 2016 09:10:06 -0800 (PST) Date: Mon, 5 Dec 2016 09:10:04 -0800 From: Stephen Hemminger To: dpreed@reed.com Cc: "Jonathan Morton" , cerowrt-devel@lists.bufferbloat.net Message-ID: <20161205091004.39423623@xeon-e3> In-Reply-To: <1480880465.82881490@apps.rackspace.com> References: <20161204082535.35E8C229@taggart.lackof.org> <1480880465.82881490@apps.rackspace.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: Re: [Cerowrt-devel] Intel latency issue X-BeenThere: cerowrt-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: Development issues regarding the cerowrt test router project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 05 Dec 2016 17:10:07 -0000 On Sun, 4 Dec 2016 14:41:05 -0500 (EST) dpreed@reed.com wrote: > The language used in the article seems confused. However, since firmware sometimes means software (the OS kernel, for example) and this is "lag under load", it's barely possible that this is bufferbloat of a sort, it seems. Would we be surprised? > > 200 ms. can also be due to interrupt mishandling, recovered by a watchdog. It's common for performance to reduce interrupt overhead by switching from interrupt driven to polled while packets are arriving at full rate and then back again when the traffic has a gap. If you don't turn interrupts back on correctly (there's a race between turning on interrupts and packet arrival after you decide and before you succeed in turning on interrupts), then you end up waiting for some "watchdog" (every 200 ms?) to handle the incoming packets. > > The idea that something actually runs for 200 ms. blocking everything seems to be the least likely situation - of course someone might have written code that held a lock while waiting for something or masked interrupts while waiting for something. But actually executing code for 200 ms.? Probably not. I have some recent experience with this hw. At my new location, the ISP provided modem was a Hitron CGNv4 which earned an F on bufferbloat. New hardware is Arris Surboard SB6190 and Linksys AC3200 which now gets all A's for bandwith, latency, and bufferbloat. The wireless is also much better.