Re: [quicwg/base-drafts] ACK generation recommendation (#3304)

mjoras <notifications@github.com> Wed, 18 December 2019 00:48 UTC

Return-Path: <noreply@github.com>
X-Original-To: quic-issues@ietfa.amsl.com
Delivered-To: quic-issues@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 7CCF312002E for <quic-issues@ietfa.amsl.com>; Tue, 17 Dec 2019 16:48:31 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -6.596
X-Spam-Level:
X-Spam-Status: No, score=-6.596 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, HTML_IMAGE_ONLY_28=1.404, HTML_MESSAGE=0.001, MAILING_LIST_MULTI=-1, RCVD_IN_DNSWL_HI=-5, SPF_HELO_NONE=0.001, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (1024-bit key) header.d=github.com
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id GQUffF3zPDea for <quic-issues@ietfa.amsl.com>; Tue, 17 Dec 2019 16:48:29 -0800 (PST)
Received: from out-20.smtp.github.com (out-20.smtp.github.com [192.30.252.203]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 6876112000F for <quic-issues@ietf.org>; Tue, 17 Dec 2019 16:48:29 -0800 (PST)
Received: from github-lowworker-5825cd4.ac4-iad.github.net (github-lowworker-5825cd4.ac4-iad.github.net [10.52.22.68]) by smtp.github.com (Postfix) with ESMTP id 816098C0097 for <quic-issues@ietf.org>; Tue, 17 Dec 2019 16:48:28 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=github.com; s=pf2014; t=1576630108; bh=iIGbjtEw774aARG4Ery9luPJOCIXHbZrU7i3QhLt2qY=; h=Date:From:Reply-To:To:Cc:In-Reply-To:References:Subject:List-ID: List-Archive:List-Post:List-Unsubscribe:From; b=fabVteY054g3a3PPZheTr67qcT5NvH54/xgZo9OhNw3FauE1SLiie6tUPB/wCVRdP T4ujq3LJk+NfXg8kI7BMBkND1q9GmwaC45Rlmglb9d54kgdx2s7NWoaG0WH0qQ7g8X FsTVP/wNduV+ZRVIUnx/8JpEx8QEFcpQ7DqcuxIA=
Date: Tue, 17 Dec 2019 16:48:28 -0800
From: mjoras <notifications@github.com>
Reply-To: quicwg/base-drafts <reply+AFTOJKZN6Z6SUJLU7HZVQHF4A2U5ZEVBNHHCAHNJCY@reply.github.com>
To: quicwg/base-drafts <base-drafts@noreply.github.com>
Cc: Subscribed <subscribed@noreply.github.com>
Message-ID: <quicwg/base-drafts/issues/3304/566815909@github.com>
In-Reply-To: <quicwg/base-drafts/issues/3304@github.com>
References: <quicwg/base-drafts/issues/3304@github.com>
Subject: Re: [quicwg/base-drafts] ACK generation recommendation (#3304)
Mime-Version: 1.0
Content-Type: multipart/alternative; boundary="--==_mimepart_5df9775c724f6_1ffb3fe0da4cd95c443b4"; charset="UTF-8"
Content-Transfer-Encoding: 7bit
Precedence: list
X-GitHub-Sender: mjoras
X-GitHub-Recipient: quic-issues
X-GitHub-Reason: subscribed
X-Auto-Response-Suppress: All
X-GitHub-Recipient-Address: quic-issues@ietf.org
Archived-At: <https://mailarchive.ietf.org/arch/msg/quic-issues/JNfO1ciA4Jnm75ElbeeSrtoA8f8>
X-BeenThere: quic-issues@ietf.org
X-Mailman-Version: 2.1.29
List-Id: Notification list for GitHub issues related to the QUIC WG <quic-issues.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/quic-issues>, <mailto:quic-issues-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/quic-issues/>
List-Post: <mailto:quic-issues@ietf.org>
List-Help: <mailto:quic-issues-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/quic-issues>, <mailto:quic-issues-request@ietf.org?subject=subscribe>
X-List-Received-Date: Wed, 18 Dec 2019 00:48:32 -0000

At Facebook, ACK handling is the largest component of what I'd call "discretionary" CPU cost (i.e. not crypto, not syscall/userspace->kernel copying). I expect that will be true in general once people have optimized their implementations. We see fine results with the suggested basic Chrome heuristic, and haven't experimented with much beyond that but it's on our roadmap. I don't think we should keep the current ACK every other in the draft as it will largely end up being facetious. Deployments will use what ends up working better in practice and we know ACKing every other is measurably problematic (I can share numbers if people are interested).

That being said, I feel uncomfortable recommending the Chrome heuristic in the draft, as it reminds me of some of the early TCP RFC's which have recommendations and constants that did not age well and are largely ignored today. Can we punt something similar to @ianswett's initial idea of having this controlled via TP or new frame type?

-- 
You are receiving this because you are subscribed to this thread.
Reply to this email directly or view it on GitHub:
https://github.com/quicwg/base-drafts/issues/3304#issuecomment-566815909