Re: Extensible Priorities and Reprioritization
Yoav Weiss <yoav@yoav.ws> Wed, 17 June 2020 09:47 UTC
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From: Yoav Weiss <yoav@yoav.ws>
Date: Wed, 17 Jun 2020 11:43:25 +0200
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To: Kazuho Oku <kazuhooku@gmail.com>
Cc: Kinuko Yasuda <kinuko@chromium.org>, Lucas Pardue <lucaspardue.24.7@gmail.com>, Patrick Meenan <patmeenan@gmail.com>, Bence Béky <bnc@chromium.org>, Eric Kinnear <ekinnear@apple.com>, Patrick Meenan <pmeenan@webpagetest.org>, HTTP Working Group <ietf-http-wg@w3.org>
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Subject: Re: Extensible Priorities and Reprioritization
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On Wed, Jun 17, 2020 at 9:55 AM Kazuho Oku <kazuhooku@gmail.com> wrote: > > > 2020年6月11日(木) 6:46 Kinuko Yasuda <kinuko@chromium.org>: > >> (Sorry, sent it too soon...) >> >> On Thu, Jun 11, 2020 at 6:12 AM Kinuko Yasuda <kinuko@chromium.org> >> wrote: >> >>> Hi all, >>> >>> Reg: reprioritization benefit I can share some recent data for Chrome. >>> For the two cases that are currently discussed I'm actually not fully sure >>> about its benefit. >>> >>> For the renderer-triggered image reprioritization cases: this is a bit >>> interesting one, we recently found two things: >>> - Delaying to start low-prio requests could often work better (partly >>> because of server-side handling) than re-prioritizing while inflight >>> - In-lab measurements (tested with top 10k real sites, both on Mobile >>> and Desktop) showed that removing in-flight re-prioritization doesn't >>> impact page load performance a lot >>> >> >> Let me stress though that testing this with servers that can properly >> handle reprioritization could change the landscape, and again this isn't >> really capturing how it affects long-lived request cases, or cases where >> tabs go foreground & background while loading, so for now I'm not very >> motivated to remove the reprioritization feature either. >> > > Hi Kinuko, > > Thank you for sharing your data. I feel a bit sad that reprioritization > isn't showing much benefit at the moment. I tend to agree that we are > likely to see different results between server implementations and HTTP > versions being used. The effectiveness of reprioritization depends on the > depth of the send buffer (after prioritization decision is made), at least > to certain extent. > FWIW, I added a flag <https://chromium-review.googlesource.com/c/chromium/src/+/2232923> to turn off Chromium's H2 request prioritization. I believe +Pat Meenan <patmeenan@gmail.com> is currently running tests with and without this flag a list of servers we estimate is likely to handle them well. > > >> >> >>> I suspect this is maybe because server-side handling is not always >>> perfect and most of requests on the web are short-lived, and this may not >>> be true for the cases where long-running requests matter. I don't have >>> data for whether may impact background / foreground cases (e.g. Chrome >>> tries to lower priorities when tabs become background) >>> >>> For download cases, Chrome always starts a new download with a low >>> priority (even if it has started as a navigation), so reprioritization >>> doesn't happen. >>> >>> Kinuko >>> >>> >>> >>> >>> >>> >>> On Wed, Jun 10, 2020 at 1:21 AM Lucas Pardue <lucaspardue.24.7@gmail.com> >>> wrote: >>> >>>> On Tue, Jun 9, 2020 at 4:27 PM Patrick Meenan <patmeenan@gmail.com> >>>> wrote: >>>> >>>>> Eric's download example is a great one for exposing the risks that >>>>> would come for an implementation that supported prioritization but not >>>>> reprioritization. >>>>> >>>>> Take the trivial example of an anchor link that links to a download >>>>> (say, a 200MB installer of some kind): >>>>> - When the user clicks on the link, the browser assumes it is doing a >>>>> navigation and issues the request with the "HTML" priority (relatively >>>>> high, possibly non-incremental >>>>> - When the response starts coming back, it has the content-disposition >>>>> to download to a file. >>>>> - At this point, the 200MB download will block every other >>>>> lower-priority request on the same connection (or possibly navigation if it >>>>> is non-incremental) >>>>> - The user clicks on another page on the same site and gets nothing or >>>>> a broken experience until the 200MB download completes >>>>> >>>>> Without reprioritization the browser will effectively have to burn the >>>>> existing QUIC connection and issue any requests on a new connection (and >>>>> repeat for each new download). >>>>> >>>>> Implementing prioritization without reprioritization in this case is >>>>> worse than having no prioritization support at all. >>>>> >>>> >>>> Thanks Eric for presenting this case, and Patrick for breaking it down. >>>> That does seem like a pretty bad outcome. >>>> >>>> Is this a good candidate for a test case? IIUC correctly the problem >>>> might occur today with HTTP/2 depending on how exclusive priorities are >>>> used. I'm curious if browsers can share any more information about what >>>> they do already. How does Firefox manage such a resource with it's priority >>>> groups? >>>> >>>> Cheers >>>> Lucas >>>> >>>> > > -- > Kazuho Oku >
- 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