[Bloat] mo bettah open source multi-party videoconferncing in an age of bloated uplinks?
sort of an outgrowth of this convo: https://lwn.net/SubscriberLink/815751/786d161d06a90f0e/ I imagine worldwide videoconferencing quality could be much better if we could convince more folk to finally install sqm or upgrade to a working docsis 3.1 solution, etc. Maybe some rag somewhere will finally pick up on bufferbloat solutions and run with it? Or we can write some articles? Or reach out to school systems? Or? I've been fiddling with jitsi, and am about to give freeswitch a try. Last I looked freeswitch's otherwise pretty nifty conference bridge didn't dynamically adjust at all due to e2e signalling, but that was years ago. (?) I have to admit that p2p multiparty videoconferencing seems more plausible in a de-bufferbloated age, but haven't explored what tools are available. (?) There's also been this somewhat entertaining convo on the ietf mbone list: https://mailarchive.ietf.org/arch/msg/mboned/2thFQk_IYn38XCZBQavhUmOd6tk/ Around me there has been this huge interest in "streaming". The user agreement for these (see restream.io's) is scary - and the copyright police have control... but I am very happy to report that even a couple really lousy long distance fq_codel'd ath9k links work *really* well (with facebook's implementation), where a non fq_codeled link (ath10k) failed miserably... and setting up a reflector in nginx also failed miserably. Anyone working on the ath10k AQL backport for openwrt as yet? -- Make Music, Not War Dave Täht CTO, TekLibre, LLC http://www.teklibre.com Tel: 1-831-435-0729 ___ Bloat mailing list Bloat@lists.bufferbloat.net https://lists.bufferbloat.net/listinfo/bloat
Re: [Bloat] [Cake] mo bettah open source multi-party videoconferncing in an age of bloated uplinks?
Congestion control for real-time video is quite different than for streaming. Streaming really is dealt with by a big enough (multi-second) buffering, and can in principle work great over TCP (if debloated). UDP congestion control MUST be end-to-end and done in the application layer, which is usually outside the OS kernel. This makes it tricky, because you end up with latency variation due to eh OS's process scheduler that is on the order of magnitude of the real-time requirements for air-to-air or light-to-light response (meaning the physical transition from sound or picture to and from the transducer). This creates a godawful mess when trying to do an app. Whether in WebRTC (peer to peer UDP) or in a Linux userspace app, the scheduler has huge variance in delay. Now getting rid of bloat currently requires TCP to respond to congestion signalling. UDP in the kernel doesn't do that, and it doesn't tell userspace much either (you can try to detect packet drops in userspace, but coding that up is quite hard because the schdulers get in the way of measurement, and forget about ECN being seen in userspace) This is OS architecture messiness, not a layer 2 or 3 issue. I've thought about this a lot. Here's my thoughts: I hate putting things in the kernel! It's insecure. But what this says is that for very historical and stupid reasons (related to the ideas of early timesharing systems like Unix and Multics) folks try to make real-time algorithms look like ordinary "processes" whose notion of controlling temporal behavior is abstracted away. So: 1. We really should rethink how timing-sensitive algorithms are expressed, and it isn't gonna be good to base them on semaphores and threads that run at random rates. That means a very different OS conceptual framework. Can this share with, say, the Linux we know and love - yes, the hardware can be shared. One should be able to dedicate virtual processors that are not running Linux processes, but instead another computational model (dataflow?). An example of this (though clunky and unsupported by good tools) is in FreeBSD, it's called *netgraph*. It's a structured way to write reactive algorithms that are demand or arrival driven. It also has some security issues, and since it is heavily based on passing mbufs around it's really quirky. But I have found it useful for the kind of things that need to get done in teleconferencing voice and video. 2. EBPF is interesting, because it is more secure, and is again focused on running code at kernel level, event-driven. I think it would be a seriously difficult lift to get it to the point where one could program the networked media processing in BPF. 3. One of the nice things about KVM (hardware virtualization) is that potentially it lets different low level machine models share a common machine. It occurs to me that using VIRTIO network devices and some kind of VIRTIO media processing devices, that a KVM virtual machine could be hooked up to the packet-level networking drivers in the end device, isolating the teleconferencing from the rest of the endpoint OS, and creating the right kind of near-bare--metal environment for managing the timing of network packets and the paths to the screen and audio that would be simple and clean and tightly scheduled. KVM could "own" one or more of the physical cores during the teleconference. You can see, though, that this isn't just a "network protocol design" problem. This is only partly a network protocol issue, but one that is coupled with the architecture of the end systems. I reminisce a little bit thinking back to the 1970's and 80's when TCP/IP and UDP/IP were being designed. Sadly, it was one of the big problems of communicating between the OS community and the protocol community that the OS community couldn't think outside the "timesharing" system box, and the protocol community thought of networking like phone calls (sessions). This is where the need for control of timing and buffering got lost. The timesharing folks largely thought of networks as for reliable timeless sequential "streams" of data that had no particular urgency. The network protocol folks were focused on ARQ. Only a few of us cared about end-to-end latency bounds (where ends meant keyboard click or audio sample to screen display change or speaker motion). The packet speech guys did, but most networking guys wanted to toss them under the bus as annoying. And those of us doing distributed multinode algorithms did, but the remote login and FTP guys were skeptical that would ever matter. It's the latency, stupid. Not the reliability, nor the consistency, nor throughput. Unless both the OS and the path are focused on minimizing latency, a vast set of applications will suck. Unfortunately, both the OS and network communities are *stuck* in a world where latency is uncontrollable, and there are no tools for getting it better. On Friday, March 27, 2020 1:2
Re: [Bloat] [Cake] mo bettah open source multi-party videoconferncing in an age of bloated uplinks?
On Fri, 27 Mar 2020, David P. Reed wrote: Congestion control for real-time video is quite different than for streaming. Streaming really is dealt with by a big enough (multi-second) buffering, and can in principle work great over TCP (if debloated). UDP congestion control MUST be end-to-end and done in the application layer, which is usually outside the OS kernel. This makes it tricky, because you end up with latency variation due to eh OS's process scheduler that is on the order of magnitude of the real-time requirements for air-to-air or light-to-light response (meaning the physical transition from sound or picture to and from the transducer). at some level this is correct, but if the link is clogged with TCP packets, it doesn't matter what your UDP application attempts to do, so installing cake to keep individual links from being too congested will allow your UDP application have a chance to operate. David Lang ___ Bloat mailing list Bloat@lists.bufferbloat.net https://lists.bufferbloat.net/listinfo/bloat
Re: [Bloat] [Cake] mo bettah open source multi-party videoconferncing in an age of bloated uplinks?
Of interest given some of what you say below, there is a huge discussion on netdev about how to best implement hardware offloads for network slicing: https://www.spinics.net/lists/netdev/msg638836.html Me, I always rolled my eyes up at all the network virtualization stuff and ran from the room, screaming, given ow much I care about low latency. The udp vs tcp offload split has been nightmare enough. That said, to this day I lack a clear idea how any multi-tenant dc operation really works, I've generally assumed it was policers, and have deployed sqm (now cake) instead on everything in the cloud that seemed to need it. On Fri, Mar 27, 2020 at 12:00 PM David P. Reed wrote: > > Congestion control for real-time video is quite different than for streaming. > Streaming really is dealt with by a big enough (multi-second) buffering, and > can in principle work great over TCP (if debloated). > > UDP congestion control MUST be end-to-end and done in the application layer, > which is usually outside the OS kernel. This makes it tricky, because you end > up with latency variation due to eh OS's process scheduler that is on the > order of magnitude of the real-time requirements for air-to-air or > light-to-light response (meaning the physical transition from sound or > picture to and from the transducer). > > This creates a godawful mess when trying to do an app. Whether in WebRTC > (peer to peer UDP) or in a Linux userspace app, the scheduler has huge > variance in delay. > > Now getting rid of bloat currently requires TCP to respond to congestion > signalling. UDP in the kernel doesn't do that, and it doesn't tell userspace > much either (you can try to detect packet drops in userspace, but coding that > up is quite hard because the schdulers get in the way of measurement, and > forget about ECN being seen in userspace) > > This is OS architecture messiness, not a layer 2 or 3 issue. > > I've thought about this a lot. Here's my thoughts: > > I hate putting things in the kernel! It's insecure. But what this says is > that for very historical and stupid reasons (related to the ideas of early > timesharing systems like Unix and Multics) folks try to make real-time > algorithms look like ordinary "processes" whose notion of controlling > temporal behavior is abstracted away. > > So: > 1. We really should rethink how timing-sensitive algorithms are expressed, > and it isn't gonna be good to base them on semaphores and threads that run at > random rates. That means a very different OS conceptual framework. Can this > share with, say, the Linux we know and love - yes, the hardware can be > shared. One should be able to dedicate virtual processors that are not > running Linux processes, but instead another computational model (dataflow?). > An example of this (though clunky and unsupported by good tools) is in > FreeBSD, it's called *netgraph*. It's a structured way to write reactive > algorithms that are demand or arrival driven. It also has some security > issues, and since it is heavily based on passing mbufs around it's really > quirky. But I have found it useful for the kind of things that need to get > done in teleconferencing voice and video. > > 2. EBPF is interesting, because it is more secure, and is again focused on > running code at kernel level, event-driven. I think it would be a seriously > difficult lift to get it to the point where one could program the networked > media processing in BPF. > > 3. One of the nice things about KVM (hardware virtualization) is that > potentially it lets different low level machine models share a common > machine. It occurs to me that using VIRTIO network devices and some kind of > VIRTIO media processing devices, that a KVM virtual machine could be hooked > up to the packet-level networking drivers in the end device, isolating the > teleconferencing from the rest of the endpoint OS, and creating the right > kind of near-bare--metal environment for managing the timing of network > packets and the paths to the screen and audio that would be simple and clean > and tightly scheduled. KVM could "own" one or more of the physical cores > during the teleconference. > > You can see, though, that this isn't just a "network protocol design" > problem. This is only partly a network protocol issue, but one that is > coupled with the architecture of the end systems. > > I reminisce a little bit thinking back to the 1970's and 80's when TCP/IP and > UDP/IP were being designed. Sadly, it was one of the big problems of > communicating between the OS community and the protocol community that the OS > community couldn't think outside the "timesharing" system box, and the > protocol community thought of networking like phone calls (sessions). This is > where the need for control of timing and buffering got lost. The timesharing > folks largely thought of networks as for reliable timeless sequential > "streams" of data that had no particular urge
Re: [Bloat] [Cake] mo bettah open source multi-party videoconferncing in an age of bloated uplinks?
I don't know to what extent the freeswitch guys would be interested in this thread. I'd like find a good list or forum to talk about the state of the art in videoconferencing ? , the ietf rmcat and webrtc lists are mostly dead. hangouts, jitsi, zoom, etc, seem to be pretty good products nowadays (at least in my fq_codel'd environment), but solid info on how to make them better in the home and for online tele-learning On Fri, Mar 27, 2020 at 12:00 PM David P. Reed wrote: > > Congestion control for real-time video is quite different than for streaming. > Streaming really is dealt with by a big enough (multi-second) buffering, and > can in principle work great over TCP (if debloated). Your encoder still has to adjust to the available bandwidth. The facebook streaming application did this beautifully through my very limited highly shared 5mbit uplink - adjusting quickly to a parallel rrul test in particular by skipping some frames. then lowering the frame rate and quality, but an early attempt of mine to merely reflect rtmp streams did not, neither an attempt with "obs studio". there was about 30 sec of delay in the facebook test - I figure some of this is tuned to visible uplink buffer sizes (still seconds over cell), but also to give the riaa a shot at censoring the audio. (a commercial song crept into - over a mic! - which was detected as infringing on one attempt which automatically muted the audio and keyed a nastygram from fb) I'm going to poke into obs studios underlying code (rtsp anyone?0 at some point, and really - udp with a head dropping aqm is the best thing for transporting video, IMHO. > UDP congestion control MUST be end-to-end and done in the application layer, > which is usually outside the OS kernel. This makes it tricky, because you end > up with latency variation due to eh OS's process scheduler that is on the > order of magnitude of the real-time requirements for air-to-air or > light-to-light response (meaning the physical transition from sound or > picture to and from the transducer). We are so far from that point! encoder latencies today are in the 100+ms range. I always liked the opus codec because it can get down to 2.7ms encoding latencies, and a doubled frame rate camera 8ms but video encoding rates Im out of date on. (?) One long deferred piece of webrtc/rmcat research I always meant to do was audio and video on separate ports in the stream, and using that 2.7m opus clock and depending on fq at the bottleneck to provide better congestion control information by treating the smaller audio packets as a clock signal. Due to lack of port space and a widespread perception that fq isn't out there, most videoconferencing streams multiplex everything over the same port. With ipv6 in place, well, port space is no longer a problem. > > This creates a godawful mess when trying to do an app. Whether in WebRTC > (peer to peer UDP) or in a Linux userspace app, the scheduler has huge > variance in delay. I figure the bounding scheduler latency is still well manageable below a single 60fps frame. > Now getting rid of bloat currently requires TCP to respond to congestion > signalling. UDP in the kernel doesn't do that, and it doesn't tell userspace > much either (you can try to detect packet drops in userspace, but coding that > up is quite hard because the schdulers get in the way of measurement, and > forget about ECN being seen in userspace) ECN in userspace is easy on udp, except that most api's tend to abstract into a file handle style abstraction and a single return of data, not control information, and the api for getting tos options ugly. APIs that can return data and info (data, packetheader) = getudp_someway() probably exist for more modern languages like go, but rarely c or c++. Totally out of date on this, last I looked at the google congestion congtrol code bae was in mozilla... 8 years ago! As for doing udp semi-efficiently in batches... sendmmsg, recvmmsg is a rather underused kernel api. And ugly as sin. With some major limitations. > > This is OS architecture messiness, not a layer 2 or 3 issue. To me the nightmare starts with most cpu context switch latencies being 1000s of clocks nowadays. > > I've thought about this a lot. Here's my thoughts: > > I hate putting things in the kernel! It's insecure. But what this says is > that for very historical and stupid reasons (related to the ideas of early > timesharing systems like Unix and Multics) folks try to make real-time > algorithms look like ordinary "processes" whose notion of controlling > temporal behavior is abstracted away. On the whole, with the rise of quic - in particular quic, as multiple userspace libs have been emerging - we've got good bases to move forward with more stuff in userspace. > > So: > 1. We really should rethink how timing-sensitive algorithms are expressed, > and it isn't gonna be good to base them on semaphores and threads that run at > random rates. That means a
Re: [Bloat] [Cake] mo bettah open source multi-party videoconferncing in an age of bloated uplinks
> I hate putting things in the kernel! It's insecure. But what this says is > that for very historical and stupid reasons (related to the ideas of early > timesharing systems like Unix and Multics) folks try to make real-time > algorithms look like ordinary "processes" whose notion of controlling > temporal behavior is abstracted away. Could you please say more. Why doesn't it work to put the time critical stuff in a separate light weight thread and give it higher priority than the stuff that needs lots of CPU? Is the problem in the scheduler? Is background junk overloading the system? (Are people rebuilding the kernel while video converencing?) Is it too hard to split out the logic that would go in the light weight thread? (get tangled on locks or such) -- These are my opinions. I hate spam. ___ Bloat mailing list Bloat@lists.bufferbloat.net https://lists.bufferbloat.net/listinfo/bloat
[Bloat] fcc's coronovirus guidelines
"put everyone on a schedule"... sigh https://www.fcc.gov/home-network-tips-coronavirus-pandemic -- Make Music, Not War Dave Täht CTO, TekLibre, LLC http://www.teklibre.com Tel: 1-831-435-0729 ___ Bloat mailing list Bloat@lists.bufferbloat.net https://lists.bufferbloat.net/listinfo/bloat
Re: [Bloat] fcc's coronovirus guidelines
--On Friday, March 27, 2020 3:41 PM -0700 Dave Taht wrote: "put everyone on a schedule"... sigh https://www.fcc.gov/home-network-tips-coronavirus-pandemic How do we educate officials? It's not clear who we'd even address a correction to. Is there a bufferbloat page we can point them to? ___ Bloat mailing list Bloat@lists.bufferbloat.net https://lists.bufferbloat.net/listinfo/bloat
[Bloat] Windows 10 updates multhread limit Feature request to Microsoft
I don't know if the Windows 10 updates multithreading problem is still relevant for many users, but it certainly still affects me as user with low bufferbloat, low latency, and only moderate bandwidth (50mbit , 4ms idle, ~9ms loaded) In any case, I have submitted official feedback to microsoft, as I've exhausted any possible workarounds on my end short of implementing a Windows update cache server on my LAN (go figure, apparently the cache servers download with a small number of threads). After posting this link -- I'm done advocating for this issue. I think valve steam has made some improvements, they still use many threads, but somehow, it doesn't create as many issues.There seems to be no interest in most discussion forums to explore this with any depth -- or even admit that 20 connections to 1-2 servers is problematic. Feedback hub link https://aka.ms/AA7zg1r ___ Bloat mailing list Bloat@lists.bufferbloat.net https://lists.bufferbloat.net/listinfo/bloat
