Return-Path: 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 EC5711286D9 for ; Wed, 7 Nov 2018 01:01:05 -0800 (PST) X-Virus-Scanned: amavisd-new at amsl.com X-Spam-Flag: NO X-Spam-Score: -8.47 X-Spam-Level: X-Spam-Status: No, score=-8.47 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.47, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, HTML_MESSAGE=0.001, MAILING_LIST_MULTI=-1, RCVD_IN_DNSWL_HI=-5, 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 UDqVl7PWOnYt for ; Wed, 7 Nov 2018 01:00:59 -0800 (PST) Received: from out-7.smtp.github.com (out-7.smtp.github.com [192.30.252.198]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 09128123FFD for ; Wed, 7 Nov 2018 01:00:59 -0800 (PST) Date: Wed, 07 Nov 2018 01:00:57 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=github.com; s=pf2014; t=1541581258; bh=M5QZMGM28F67nccsgGie4iJN2ekXFldcUthjy7Uk0Oo=; h=Date:From:Reply-To:To:Cc:In-Reply-To:References:Subject:List-ID: List-Archive:List-Post:List-Unsubscribe:From; b=ZXedunjweMZ/DER4/LZt1RSDkCMAkdvZfF80omgHaOsFOxWCm+LPAsfAc+Dqus1Tl gcVfK6z3o3wlChgaHoND4KLaoEUw+VJ9fxH5clAQGJ/sTR04yMG91vuDomA27BhGuc HJ6dAwgCNPqWyggIBRC94cQEe9FKRdLp0LY71NmM= From: Bob Briscoe Reply-To: quicwg/base-drafts To: quicwg/base-drafts Cc: Subscribed Message-ID: In-Reply-To: References: Subject: Re: [quicwg/base-drafts] Sender-Controlled Delayed ACK Ratio (#1978) Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="--==_mimepart_5be2a9c916e2b_9683f922ccd45bc763795"; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: list X-GitHub-Sender: bbriscoe X-GitHub-Recipient: quic-issues X-GitHub-Reason: subscribed X-Auto-Response-Suppress: All X-GitHub-Recipient-Address: quic-issues@ietf.org Archived-At: X-BeenThere: quic-issues@ietf.org X-Mailman-Version: 2.1.29 List-Id: Notification list for GitHub issues related to the QUIC WG List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 07 Nov 2018 09:01:06 -0000 ----==_mimepart_5be2a9c916e2b_9683f922ccd45bc763795 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit ### Some scenarios where the sender's preferred ack_ratio changes through the connection: 1. A sender CC that wants the receiver to turn off DelAcks during flow-start (e.g. it's using hybrid slow-start as in Cubic and wants to get delay measurements more frequently) sets ack_exp=0 during flow-start (ack_ratio=1), then increases ack_exp during congestion avoidance. If it goes idle, then re-starts, it would set ack_exp=0 again. Note on heuristics: A Linux TCP receiver currently uses a heuristic to determine when the sender has exited slow-start. However, heuristics -> ossification. A Linux receiver's heuristic only works with the current pattern of slow-start. In TCP, when we tried to improve the pattern on the sender (paced chirping), the heuristic on the receiver killed us. 2. Imagine a paced sender has hardware generic receive offload (GRO), so for a long-running flow it doesn't want a high rate of QUIC ACKs that are opaque to GRO. Let's say it would prefer at least 8 ACKs per RTT. Again, it starts with ack_exp=0, but in congestion avoidance it would use: > ack_ratio <= cwnd_in_packets/8 So calculation of ack_ratio lends itself to fast integer arithmetic. Upshot: By remote controlling the receiver, the server offloads nearly all the ACKs from large downloads, but still focuses its ACK-receiving resources on getting each client up to speed. -- 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/1978#issuecomment-436552267 ----==_mimepart_5be2a9c916e2b_9683f922ccd45bc763795 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable

Some scenarios where the sender's preferred ack_ratio changes through= the connection:

  1. A sender CC that wants the receiver to turn off DelAcks during flow-st= art (e.g. it's using hybrid slow-start as in Cubic and wants to get delay= measurements more frequently) sets ack_exp=3D0 during flow-start (ack_ra= tio=3D1), then increases ack_exp during congestion avoidance. If it goes = idle, then re-starts, it would set ack_exp=3D0 again.

    Note on heuristics: A Linux TCP receiver currently uses a heuristic to= determine when the sender has exited slow-start. However, heuristics -&g= t; ossification. A Linux receiver's heuristic only works with the curren= t pattern of slow-start. In TCP, when we tried to improve the pattern on = the sender (paced chirping), the heuristic on the receiver killed us.

    =

  2. Imagine a paced sender has hardware generic receive offload (GRO), so = for a long-running flow it doesn't want a high rate of QUIC ACKs that are= opaque to GRO. Let's say it would prefer at least 8 ACKs per RTT. Again,= it starts with ack_exp=3D0, but in congestion avoidance it would use:

ack_ratio <=3D cwnd_in_packets/8

So calculation of ack_ratio lends itself to fast integer arithmetic. 

Upshot: By remote controlling the receiver, the server offload=
s nearly all the ACKs from large downloads, but still focuses its ACK-rec=
eiving resources on getting each client up to speed.

&m= dash;
You are receiving this because you are subscribed to this thre= ad.
Reply to this email directly, view it on GitHub,= or mute the thread.3D""

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