Author Topic: sawtooth speed issues  (Read 35 times)

Narkhelek

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sawtooth speed issues
« on: December 02, 2018, 08:15:32 PM »
I keep giving qBittorrent a try because I really like it's features but I ultimately end up using something else because of speed issues that I've not been able to resolve and have persisted through many versions.  The issue I'm having is generally subpar speed and a very odd sawtooth bandwidth patterns (see the attached picture).  I will often see the speed constantly jumping between a high and low bandwidth as shown in the picture where qBittorrent is jumping between 7MBs and 1MBs.  If it wasn't for this weird sawtooth bandwidth issue where the speed is constantly dropping lowering the average throughput the speed would be fine.  I don't have this issue with any other bittorrent client.

Here is the required info:

ISP Speed is always over 250Mbs down and 12Mbs up.

I'm running on a fairly new MacBook Pro running Mojave 10.14.1.

I'm running qBittorrent 4.1.3 (64bit)

Connections: Global maximum and per torrent: 500/100
Listening port: 56516
Upload slots: Global maximum and per torrent: It shows 8/4 but I don't have either check boxed
Half-open connection value: 50
Is uTP on or off?: On
Rate limiting uTP?: Not checked
Encryption on or off?: Prefer encryption
IPv6 on or off?: Off
libtorrent version (use Help -> About -> Libraries to identify that): 1.1.9.0
Connection status? (the icon on the status bar will tell you): Don't see an icon listing this
DHT node count (on the status bar): 388
Are you using a proxy or a VPN?: Using PIA VPN



« Last Edit: December 02, 2018, 08:47:35 PM by Narkhelek »

Switeck

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Re: sawtooth speed issues
« Reply #1 on: December 02, 2018, 08:43:06 PM »
Sounds like this problem:
"Download going up and down (Mac)"    https://github.com/qbittorrent/qBittorrent/issues/8284

And similar problems:
https://github.com/qbittorrent/qBittorrent/issues/7954
https://github.com/qbittorrent/qBittorrent/issues/8759
https://github.com/qbittorrent/qBittorrent/issues/8780
(and no doubt others...)

As for your settings, I suggest a couple changes:
Lower Max connections per torrent from 100 to 50 while downloading or even as low as 10 while only seeding.
Increase global upload slots from 8 to 50.
Increase per torrent upload slots from 4 to 8.
Reduce Half-open connection value from 50 to 10. (50 is nuts even when not using a VPN or proxy, because it can cause connection instability.)

Because you're using PIA VPN, the VPN itself could partially be to blame for the speed variations -- with its buffers emptying and filling in cycles. (Google Bufferbloat for why that happens.)
Also, using a VPN or proxy may make getting incoming connections difficult to impossible. (Got a green light at bottom?)

The main problem is qBT/libtorrent definitely has speed issues, so have you set speed limits in qBT to reduce/prevent it temporarily overloading the connection and causing speed die-offs?

Narkhelek

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Re: sawtooth speed issues
« Reply #2 on: December 02, 2018, 09:03:49 PM »
Thanks for the suggestions.  I implemented all of them and it made no difference.  The weird thing is I see the same sawtooth bandwidth pattern regardless of the number of torrents active or number of peers connected.  I could have 1 torrent connected with a couple peers or 10 torrents active with hundreds of peers and I see the exact same sawtooth pattern.  This is odd since what could cause so many different transport sessions to synchronize their flows?  It's almost like there is a global synchronization issue going on (https://en.wikipedia.org/wiki/TCP_global_synchronization).  I would tend to agree that it may be an upstream issue possibly caused by PIA but I do not see this issue with any other bittorrent client or file transfer.  Maybe I'll get a pcap see if I can find anything interesting.