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Why PS4 downloads are so slow

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Re: Why PS4 downloads are so slow

#41

Post by xorblurb »

amluto wrote: post #32
ploxiln wrote: post #18

Reminds me of how Windows Vista's "Multimedia Class Scheduler Service" would put a low cap on network throughput if any sound was playing: http://www.zdnet.com/article/follow-up-playing-music-severel... Mark Russinovich justified it by explaining that the network interrupt routine was just too expensive to be able to guarantee no glitches in media playback, so it was limited to 10 packets per millisecond when any med…

I thought Windows had a fancy interrupt priority system that should, in principle, allow sound playback to preempt network interrupts? AMD64 added a fancy feature (CR8 access to the task priority register) just to accelerate interrupt prioritization. (This is all very vague memory. I know how this stuff works on Linux. Linux does not have interrupt priorities.)

Windows does not really have interrupt priorities IIRC. It kind of sort of have some, but the applicative code (device driver included) can't chose at which level they run their ISR, so its quite random whether or not the ISR you prefer should preempt others.

Plus typically general purpose OSes don't map hw interrupt priorities mechanisms to their own priorities (and very soon the hw interrupt controllers do not even know whether an ISR is running or not). I believe neither Linux nor Windows can benefit from hw assistance for interrupt priorities (and they mainly don't care at sw level anyway)

Re: Why PS4 downloads are so slow

#43

Post by xorblurb »

sharkbot wrote: post #40
amluto wrote: post #32

Earlier quoted context omitted.

I thought Windows had a fancy interrupt priority system that should, in principle, allow sound playback to preempt network interrupts? AMD64 added a fancy feature (CR8 access to the task priority register) just to accelerate interrupt prioritization. (This is all very vague memory. I know how this stuff works on Linux. Linux does not have interrupt priorities.)

I could be wrong, but my understanding of some sound cards is that they have essentially a single memory buffer that they are reading from when instructed to play a sound. Most sound cards let the OS split the buffer into two halves and raise an interrupt when one half of the buffer completes playing. Interrupt prioritization doesn't help much, because the sound data is likely being generated from user mode, and the…

Needing to wake up usermode is not necessarily an insurmountable obstacle; under Linux you can use a PREEMPT config. Storming a network card having unwanted consequences can also be mitigated: under Linux you have some network device driver that use an hybrid interrupt/polling approach with the NAPI. Combining both should theoretically allow a system to generate sound smoothly in the described conditions.

Re: Why PS4 downloads are so slow

#44

Post by toast0 »

lossolo wrote: post #22

DNS based GEO load balancing/CDN's are wrong idea today. For example if you use DNS that has bad configuration or one that is not supplied by your ISP, then you could be routed to servers thousands km/miles from your location. Last time I've checked akamai used that flawed dns based system. What you want to use now is what for example cloudflare uses which is anycast IP. You just announce same IP class on multiple ro…

As with all things, there are tradeoffs. As you say, GEO DNS doesn't work very well when the authoritative server doesn't get enough information to give a good answer; for example, if all of a nationwide ISP uses the same pool of recursive DNS, and doesn't proved EDNS client subnet, the authoritative server will not get any signal about where in the country the users are. Or, if you use DNS servers in another country for some reason, you may be assumed to be nearby to that country.

Anycast isn't perfect either though. It may be more likely to get you a route with fewer hops, but that's not necessarily the lowest latency link. And if there's a congested link in the path, it's much harder to steer a portion of users, but not all to alternate servers. You also have to deal with the potential of routing changing from packet to packet, and potentially different locations getting different parts of the same connection. It's not 'just announce the same IPs from multiple locations' and take a nap.

Anyway, unless you have thousands of datacenters well distributed throughout the globe, a lot of people are going to have high latency to whatever server is chosen, and high latency and very small windows == poor throughput, regardless of how you get to a server.

Re: Why PS4 downloads are so slow

#45

Post by [deleted] »

lossolo wrote: post #22

DNS based GEO load balancing/CDN's are wrong idea today. For example if you use DNS that has bad configuration or one that is not supplied by your ISP, then you could be routed to servers thousands km/miles from your location. Last time I've checked akamai used that flawed dns based system. What you want to use now is what for example cloudflare uses which is anycast IP. You just announce same IP class on multiple ro…

[deleted]

Re: Why PS4 downloads are so slow

#46

Post by matthewbauer »

g09980 wrote: post #36

Want to see something like this for (Apple's) App Store. Downloads are fast, but the App Store experience itself is so, so slow. Takes maybe five seconds to load search results or reviews even on a wi-fi connection.

I've noticed this too but it seems to be the same thing on both macOS and iOS, maybe it's on the server end?

Re: Why PS4 downloads are so slow

#47

Post by cm2187 »

ploxiln wrote: post #18

Reminds me of how Windows Vista's "Multimedia Class Scheduler Service" would put a low cap on network throughput if any sound was playing: http://www.zdnet.com/article/follow-up-playing-music-severel... Mark Russinovich justified it by explaining that the network interrupt routine was just too expensive to be able to guarantee no glitches in media playback, so it was limited to 10 packets per millisecond when any med…

Reminds me of Apple's Jim Reekes "engineers are retarded".

https://m.youtube.com/watch?v=C5d151lqJsA

(The annecdote really starts at 2:30).

Re: Why PS4 downloads are so slow

#48

Post by tgb »

Sorry for the newbie question, but can someone explain why the round trip time is so important for transfer speeds? From the formula I'm guessing something like this happens: server sends DATA to client, client receives DATA then sends ACK to server, server receives ACK and then finally goes ahead and sends DATA2 to the client. But TCP numbers their packets and so I would expect them to continue sending new packets while waiting for ACKs of old packets, and my reading of Wikipedia agrees. So what causes the RTT dependence in the transfer rate?

Re: Why PS4 downloads are so slow

#50

Post by stordoff »

MBCook wrote: post #16
tortasaur wrote: post #14

Earlier quoted context omitted.

I want that, as it normalizes the need for large upload bandwidth. The only reason it's such a scarce commodity now is that households aren't perceived as needing that bandwidth. The proliferation of legal peer-to-peer systems will hopefully drive the spread of symmetric connections.

One of the reasons I switched off of AT&T uVerse is they seemed to give you the absolute minimum upload bandwidth needed to achieve the advertised download bandwidth. So if you were downloading or streaming and uploaded anything more than a small image your download speed would plummet as you ran out of upstream bandwidth. Online backups/syncing? Hope you're not trying to do anything else that requires bandwidth.

> Hope you're not trying to do anything else that requires bandwidth.

I get the same on Sky (UK) ADSL (fibre[TTC] seems to be unaffected). When I'm uploading e.g. a video to YouTube, even something like Hacker News will often time out.

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