Re: Priority implementation complexity (was: Re: Extensible Priorities and Reprioritization)
Yoav Weiss <yoav@yoav.ws> Mon, 15 June 2020 12:55 UTC
Return-Path: <ietf-http-wg-request+bounce-httpbisa-archive-bis2juki=lists.ie@listhub.w3.org>
X-Original-To: ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com
Delivered-To: ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id A8AB13A0D5D for <ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com>; Mon, 15 Jun 2020 05:55:06 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -2.648
X-Spam-Level:
X-Spam-Status: No, score=-2.648 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, HEADER_FROM_DIFFERENT_DOMAINS=0.249, HTML_MESSAGE=0.001, MAILING_LIST_MULTI=-1, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=ham autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (2048-bit key) header.d=yoav-ws.20150623.gappssmtp.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 zUMGU32L2h1d for <ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com>; Mon, 15 Jun 2020 05:55:03 -0700 (PDT)
Received: from lyra.w3.org (lyra.w3.org [128.30.52.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 7B0633A0D5C for <httpbisa-archive-bis2Juki@lists.ietf.org>; Mon, 15 Jun 2020 05:55:03 -0700 (PDT)
Received: from lists by lyra.w3.org with local (Exim 4.92) (envelope-from <ietf-http-wg-request@listhub.w3.org>) id 1jkob9-0003W8-8Z for ietf-http-wg-dist@listhub.w3.org; Mon, 15 Jun 2020 12:52:23 +0000
Resent-Date: Mon, 15 Jun 2020 12:52:23 +0000
Resent-Message-Id: <E1jkob9-0003W8-8Z@lyra.w3.org>
Received: from titan.w3.org ([128.30.52.76]) by lyra.w3.org with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from <yoav@yoav.ws>) id 1jkob7-0003VM-TE for ietf-http-wg@listhub.w3.org; Mon, 15 Jun 2020 12:52:21 +0000
Received: from mail-lf1-x129.google.com ([2a00:1450:4864:20::129]) by titan.w3.org with esmtps (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from <yoav@yoav.ws>) id 1jkob4-0001M0-VD for ietf-http-wg@w3.org; Mon, 15 Jun 2020 12:52:21 +0000
Received: by mail-lf1-x129.google.com with SMTP id d27so4883603lfq.5 for <ietf-http-wg@w3.org>; Mon, 15 Jun 2020 05:52:18 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yoav-ws.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=YhD860bfb4+kXxMgxj7b6WtVaDclGtH+STcRSsUELRU=; b=Bg2tS+jpyLCGqJ+LOlCZpFKvOyD7QiyuCN7us4DpDQith6sUbdETgcIZNWMns0G3LU UgMInspTktdcSA6mMDTNssTm6S3nWS43OmLJIp0FHFVYzHxVKWA0MPYUQ7jOxJckz/O7 p01zuifmRc8+ZO6CkWZQrY9VlnU72of/eEZV0lNtU4XEUAguX3cKWt/0TZssfG93RvJp nk71ZOOVBXBmAznzVy3CXxM8WjG0OotNdmgNElqOTiu9FN1x/Ca/+Mcb/LSeXgpnYa6Z l2X04v8b5DgxzzePl1LcR7c0EteFTXPfPce6W4chBIln41DLJ5fD+KFVjp/uMgKtpqFx E8iQ==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=YhD860bfb4+kXxMgxj7b6WtVaDclGtH+STcRSsUELRU=; b=SZNoIMT2fqb+1tsnVI3+SB0DbUYFwt+zQig/nB51Il0Q1Pp+vp7IN7JiXa6D40EqB+ 5+EZR+KRR8SOTkbpRON8kYAJs/wyN+7GdT4hyBdq0VtOUfnvYXUmhYPqMtrq74mrozqz Kp4ZEyYJJMJ4nGJ55UApd0KLjWGOMib3mPnZ9nsSzn7UD18zYxIvuA/nEY7kNXfJR26e gnsF06YP9BdrRc5F9NjBB3gz6xIiXIK2u/UttBY1QbwYpD+DabkkoA80+/lyF+6C8LtZ c5/GFaoiUWnaw/rTdjT4kaTsLTuo5X/gDfGkB7nIWeQ16qo2FH4FiTv5BBmSyKxVer7V NSYg==
X-Gm-Message-State: AOAM533t5/GVz/BJIOQvYtG1OQh7WjXjP2MgivO7JbOywx3jgjl2d6oq dr6s9/hE3wSt3i0N21c9TNIpxwGW+Zpjy+SglrNE2g==
X-Google-Smtp-Source: ABdhPJzo2mnuOOLEpPCO7FM2rmMT5hT/q71QWBUa5kRE2PLpyzGNDSn21WkijLKc1/bg9iTIUS/R3/5WQNml1X4nsss=
X-Received: by 2002:a05:6512:7b:: with SMTP id i27mr13707768lfo.30.1592225525879; Mon, 15 Jun 2020 05:52:05 -0700 (PDT)
MIME-Version: 1.0
References: <CALGR9obRjBSADN1KtKF6jvFVzNS1+JzaS0D0kCVKHKkd4sn+MQ@mail.gmail.com> <459C86F8-A989-4EF4-84DC-3568FF594F36@apple.com> <CANatvzwSpSHd7kZD-4tyMGkBJDdCBi6r_pLBvnaT8rrQy6SBHQ@mail.gmail.com> <CACMu3treK0m2mbpw9FebOjOcEed0bW-DbLbryHJH1DWAHoz+9g@mail.gmail.com> <CALGR9oZgE7ZfXdoYdUh9LUYC1fi8fMUyyTpvmV3GF7Z6Oxgg1g@mail.gmail.com> <20200609144428.GC22180@lubuntu> <CAJV+MGyuhxx=P6kZKktuREeq5pipZjxmwWP4jE_Sxhj_+krU2Q@mail.gmail.com> <CANatvzx_eg84V7UefOtSF+NHGHnTg7h-9n5bsRZRXxBqsaOkfQ@mail.gmail.com> <CACj=BEip6+7AunFsD=6qM5rsgrTfg6bRctOMu1gOe-KVjAW7Dw@mail.gmail.com> <CANatvzyv03VH9=+J=M2yY0EwCXp7HMWsXYaXOE=WYGDKBHdaVA@mail.gmail.com> <2C53D8AF-EFA8-42A3-9666-955A054468DB@greenbytes.de> <CACj=BEic2qzMXEfcsKS9CYnowChc-kMRjH66d3uKs+pqTz9Fug@mail.gmail.com> <4E0E8032-A903-46A2-A131-F1F4DE3CC037@greenbytes.de> <CACj=BEjOC-8S38U36Jw+Yb7yH_BZjxBkeLE6dLWH=8VMyBW80Q@mail.gmail.com> <ECF2C350-5D53-4E3B-9AAC-2F7E3FD4B528@greenbytes.de> <CACj=BEh53ZWj1UV6tNDaWPiuHbmbVmkYimu_rdYcYm06dZJAAQ@mail.gmail.com> <CAJV+MGzesbFRZFGK5SUM70HJrx3fdJ8AAGGqmwqDQhrL3eFmUw@mail.gmail.com>
In-Reply-To: <CAJV+MGzesbFRZFGK5SUM70HJrx3fdJ8AAGGqmwqDQhrL3eFmUw@mail.gmail.com>
From: Yoav Weiss <yoav@yoav.ws>
Date: Mon, 15 Jun 2020 14:51:49 +0200
Message-ID: <CACj=BEiVPfOPGPuSu-tx5AovWwvTEwjCTqEooMq2muEteHZLAw@mail.gmail.com>
To: Patrick Meenan <patmeenan@gmail.com>
Cc: Bence Béky <bnc@chromium.org>, HTTP Working Group <ietf-http-wg@w3.org>, Kazuho Oku <kazuhooku@gmail.com>, Lucas Pardue <lucaspardue.24.7@gmail.com>, Stefan Eissing <stefan.eissing@greenbytes.de>
Content-Type: multipart/alternative; boundary="000000000000df674d05a81ee403"
Received-SPF: pass client-ip=2a00:1450:4864:20::129; envelope-from=yoav@yoav.ws; helo=mail-lf1-x129.google.com
X-W3C-Hub-Spam-Status: No, score=-8.9
X-W3C-Hub-Spam-Report: BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, W3C_AA=-1, W3C_DB=-1, W3C_IRA=-1, W3C_IRR=-3, W3C_WL=-1
X-W3C-Scan-Sig: titan.w3.org 1jkob4-0001M0-VD 5886b54bcefe77a9b59c49bcecd48eae
X-Original-To: ietf-http-wg@w3.org
Subject: Re: Priority implementation complexity (was: Re: Extensible Priorities and Reprioritization)
Archived-At: <https://www.w3.org/mid/CACj=BEiVPfOPGPuSu-tx5AovWwvTEwjCTqEooMq2muEteHZLAw@mail.gmail.com>
Resent-From: ietf-http-wg@w3.org
X-Mailing-List: <ietf-http-wg@w3.org> archive/latest/37767
X-Loop: ietf-http-wg@w3.org
Resent-Sender: ietf-http-wg-request@w3.org
Precedence: list
List-Id: <ietf-http-wg.w3.org>
List-Help: <https://www.w3.org/Mail/>
List-Post: <mailto:ietf-http-wg@w3.org>
List-Unsubscribe: <mailto:ietf-http-wg-request@w3.org?subject=unsubscribe>
On Mon, Jun 15, 2020 at 2:10 PM Patrick Meenan <patmeenan@gmail.com> wrote: > Even without a priority tree it is likely that the H3 extensible > priorities structure would cause not-yet-started responses to need to be > scheduled ahead of in-flight responses. The urgency value is effectively a > parent/child relationship. > I wouldn't consider the inflight response dependent on the not-yet-started one here, because the not-yet-started one doesn't need a specific response to hold for it, it just needs *any* response to finish (and free up a worker thread in the architecture Stefan outlined) in order to be sent (with its appropriate priority). So, it might be somewhat delayed, but won't be held back forever if a specific response is a long sending one. (assuming the number of worker thread is not very small) > It's not as unbounded as H2 but if you churned through a bunch of > reprioritizations with stalled streams you could cause issues for a server > that didn't protect against it. > > Limiting the reprioritizations to "what stream to pick next" would help > but wouldn't solve the long download problem. > > On Mon, Jun 15, 2020 at 7:44 AM Yoav Weiss <yoav@yoav.ws> wrote: > >> >> >> On Mon, Jun 15, 2020 at 1:18 PM Stefan Eissing < >> stefan.eissing@greenbytes.de> wrote: >> >>> >>> Stefan Eissing >>> >>> <green/>bytes GmbH >>> Hafenweg 16 >>> <https://www.google.com/maps/search/Hafenweg+16+%0D%0A48155+M%C3%BCnster?entry=gmail&source=g> >>> 48155 Münster >>> <https://www.google.com/maps/search/Hafenweg+16+%0D%0A48155+M%C3%BCnster?entry=gmail&source=g> >>> www.greenbytes.de >>> >>> > Am 15.06.2020 um 12:14 schrieb Yoav Weiss <yoav@yoav.ws>: >>> > >>> > >>> > >>> > On Mon, Jun 15, 2020 at 11:03 AM Stefan Eissing < >>> stefan.eissing@greenbytes.de> wrote: >>> > >>> > > Am 15.06.2020 um 10:28 schrieb Yoav Weiss <yoav@yoav.ws>: >>> > > >>> > > >>> > > >>> > > On Mon, Jun 15, 2020 at 9:55 AM Stefan Eissing < >>> stefan.eissing@greenbytes.de> wrote: >>> > > > Am 11.06.2020 um 10:41 schrieb Kazuho Oku <kazuhooku@gmail.com>: >>> > > > >>> > > > That depends on how much clients would rely on reprioritization. >>> Unlike H2 priorities, Extensible Priority does not have inter-stream >>> dependencies. Therefore, losing *some* prioritization signals is less of an >>> issue compared to H2 priorities. >>> > > > >>> > > > Assuming that reprioritization is used mostly for refining the >>> initial priorities of a fraction of all the requests, I think there'd be >>> benefit in defining reprioritization as an optional feature. Though I can >>> see some might argue for not having reprioritization even as an optional >>> feature unless there is proof that it would be useful. >>> > > >>> > > >>> > > > We should decide if reprioritization is good or bad, based on as >>> much data as we can pull, and make sure it's implemented only if we see >>> benefits for it in some cases, and then make sure it's only used in those >>> cases. >>> > > >>> > > When thinking about priority implementations, I recommend thinking >>> about a H3 reverse proxy in front of a legacy H1 server. Assume limited >>> memory, disk space and backend connections. >>> > > >>> > > (Re-)prioritization in H2 works well for flow control, among the >>> streams that have response data to send. Priorities can play a part in >>> server scheduling, but >>> > > it's more tricky. By "scheduling" I mean that the server has to pick >>> one among the opened streams for which it wants to compute a response for. >>> This is often impossible to re-prioritize afterwards (e.g. suicidal for a >>> server implementation). >>> > > >>> > > Can you expand on why it is "suicidal"? >>> > >>> > It is tricky to obey re-prioritizations to the letter, managing >>> memory+backend connections and protecting the infrastructure against DoS >>> attacks. The reality is that there are limited resources and a server is >>> expected to protect those. It's a (pun intended) top priority. >>> > >>> > Another priority topping the streams is the concept of fairness >>> between connections. In Apache httpd, the resources to process h2 streams >>> are foremost shared evenly between connections. >>> > >>> > That makes sense. Would re-prioritization of specific streams somehow >>> require to change that? >>> > >>> > The share a connection gets is then allocated to streams based on >>> current h2 priority settings. Any change after that will "only" affect the >>> downstream DATA allocation. >>> > >>> > I *think* this makes sense as well, assuming that by "downstream" you >>> mean "future". Is that what you meant? Or am I missing something? >>> > >>> > Also, the number of "active" streams on a connection is dynamic. It >>> will start relatively small and grow if the connection is well behaving, >>> shrink if it is not. That one of the reasons that Apache was only partially >>> vulnerable to a single issue on the Netflix h2 cve list last year (the >>> other being nghttp2). >>> > >>> > tl;dr >>> > >>> > By "suicidal" I mean a server failing the task of process thousands of >>> connections in a consistent and fair manner. >>> > >>> > Apologies if I'm being daft, but I still don't understand how >>> (internal to a connection) stream reprioritization impacts cross-connection >>> fairness. >>> >>> *fails to imagine Yoav as being daft* >>> >> :) >> >> Thanks for outlining the server-side processing! >> >> >>> A server with active connections and workers. For simplicity, assume >>> that each ongoing request allocates a worker. >>> - all workers are busy >>> - re-prio arrives and makes a stream A, being processed, depend on a >>> stream B which has not been assigned a worker yet. >>> >> >> OK, I now understand that this can be concerning. >> IIUC, this part is solved by with Extensible Priorities (because there's >> no dependency tree). >> >> Lucas, Kazuho - can you confirm? >> >> >>> - ideally, the server would freeze the processing of A and assign the >>> resources to B. >>> - however re-allocating the resources is often not possible (Imagine a >>> CGI process running or a backend HTTP/1.1 or uWSGI connection.) >>> - the server can only suspend the worker or continue processing, >>> ignoring the dependency. >>> - a suspended worker is very undesirable and a possible victim of a >>> slow-loris attack >>> - To make this suspending less sever, the server would need to make >>> processing of stream B very important. To unblock it quickly again. This is >>> then where unfairness comes in. >>> >>> The safe option therefore is to continue processing stream A and ignore >>> the dependency on B. Thus, priorities are only relevant: >>> 1. when the next stream to process on a connection is selected >>> 2. when size/number of DATA frames to send is allocated on a connection >>> between all streams that want to send >>> >>> (Reality is often not quite as bad as I described: when static >>> file/cache resources are served for example, a worker often just does the >>> lookup, producing a file handle very quickly. A connection easily juggles a >>> number of file handles to stream out according to priorities and stalling >>> one file on another comes at basically no risk and cost.) >>> >>> Now, this is for H2 priorities. I don't know enough about QUIC >>> priorities to have an opinion on the proposals. Just wanted to point out >>> that servers see the world a little different than clients. ;) >>> >> >> I checked and it seems like Chromium does indeed change the parent >> dependency as part of reprioritization. If the scenario you outlined is a >> problem in practice, we should discuss ways to avoid doing that with H2 >> priorities. >> >> >>> >>> Cheers, Stefan >>> >>> >>> > > >>> > > >>> > > If we would do H2 a second time, my idea would be to signal >>> priorities in the HTTP request in a connection header and use this in the >>> H2 frame layer to allocate DATA space on the downlink. Leave out changing >>> priorities on a request already started. Let the client use its window >>> sizes if it feels the need. >>> > > >>> > > Cheers, Stefan (lurking) >>> > >>> >>>
- Extensible Priorities and Reprioritization Lucas Pardue
- Re: Extensible Priorities and Reprioritization Yoav Weiss
- Re: Extensible Priorities and Reprioritization Lucas Pardue
- Re: Extensible Priorities and Reprioritization Patrick Meenan
- Re: Extensible Priorities and Reprioritization Lucas Pardue
- Re: Extensible Priorities and Reprioritization Yoav Weiss
- Re: Extensible Priorities and Reprioritization Eric Kinnear
- Re: Extensible Priorities and Reprioritization Kazuho Oku
- Re: Extensible Priorities and Reprioritization Martin Thomson
- Re: Extensible Priorities and Reprioritization Bence Béky
- Priority implementation complexity (was: Re: Exte… Lucas Pardue
- Re: Priority implementation complexity (was: Re: … Dmitri Tikhonov
- Re: Priority implementation complexity (was: Re: … Patrick Meenan
- Re: Extensible Priorities and Reprioritization Patrick Meenan
- Re: Extensible Priorities and Reprioritization Lucas Pardue
- Re: Priority implementation complexity (was: Re: … Lucas Pardue
- Re: Priority implementation complexity (was: Re: … Dmitri Tikhonov
- Re: Priority implementation complexity (was: Re: … Roy T. Fielding
- Re: Extensible Priorities and Reprioritization Kinuko Yasuda
- Re: Extensible Priorities and Reprioritization Kinuko Yasuda
- Re: Priority implementation complexity (was: Re: … Kazuho Oku
- Re: Priority implementation complexity (was: Re: … Yoav Weiss
- Re: Priority implementation complexity (was: Re: … Martin Thomson
- Re: Priority implementation complexity (was: Re: … Kazuho Oku
- Re: Priority implementation complexity (was: Re: … Stefan Eissing
- Re: Priority implementation complexity (was: Re: … Yoav Weiss
- Re: Priority implementation complexity (was: Re: … Stefan Eissing
- Re: Priority implementation complexity (was: Re: … Yoav Weiss
- Re: Priority implementation complexity (was: Re: … Stefan Eissing
- Re: Priority implementation complexity (was: Re: … Yoav Weiss
- Re: Priority implementation complexity (was: Re: … Patrick Meenan
- Re: Priority implementation complexity (was: Re: … Yoav Weiss
- Re: Priority implementation complexity (was: Re: … Patrick Meenan
- Re: Priority implementation complexity (was: Re: … Kazuho Oku
- Re: Priority implementation complexity (was: Re: … Yoav Weiss
- Re: Priority implementation complexity (was: Re: … Barry Pollard
- Re: Priority implementation complexity (was: Re: … Barry Pollard
- Re: Extensible Priorities and Reprioritization Kazuho Oku
- Re: Extensible Priorities and Reprioritization Yoav Weiss
- Re: Priority implementation complexity (was: Re: … Lucas Pardue
- Re: Priority implementation complexity (was: Re: … Tom Bergan
- Re: Priority implementation complexity (was: Re: … Lucas Pardue
- Re: Priority implementation complexity (was: Re: … Tom Bergan
- Re: Priority implementation complexity (was: Re: … Lucas Pardue
- Re: Extensible Priorities and Reprioritization Patrick Meenan
- Re: Extensible Priorities and Reprioritization Patrick Meenan
- Re: Extensible Priorities and Reprioritization Lucas Pardue
- Reprioritization - implementation intent Mark Nottingham
- Re: Reprioritization - implementation intent Eric Kinnear
- Nice to have guidance (was: Re: Reprioritization … Lucas Pardue
- Re: Nice to have guidance (was: Re: Reprioritizat… Eric Kinnear
- Re: Reprioritization - implementation intent Yoav Weiss
- Re: Reprioritization - implementation intent Yoav Weiss
- Re: Reprioritization - implementation intent Yoav Weiss