Re: Priority, Speed

On Apr 25, 2006, at 09:28, Florin Braghis wrote:

> Hi,
> I have several questions:
>
>
> 1. Priority
> For a torrent with multiple files, is there a way to specify the  
> priority of the files being downloaded ?

Not for the moment. Right now one can only choose to download or not  
download certain files.

However, I have been experimenting some with generalizing the  
priority concept to not only be based on rarity. For the moment  
mostly for downloading popular pieces in sequence.

>  2. Speed
> a) When starting a download from one peer, it seems that the  
> download doesn't start at full speed, but gradually increases.
> It can take up to 30 seconds for a download to reach 1Mb/s on a LAN.
> Is there a way to remove/disable this limitation ?

The TCP slow-start would probably account for about 2 seconds I  
guess. The main reason is probably the function in libtorrent that  
adjusts the download queue size depending on download speed. The plan  
is to make it configurable, but right now it's hardcoded. The number  
of out standing requests is linearly dependent on the download speed  
from that peer. The constant should probably be increased there then.

I haven't really tested libtorrent in a 100Mbit/s setting, so any  
input is very welcome.

If you're using 0.9.2 (cvs, 'libtorrent_asio' branch) you could try  
tweaking the desired request queue time, line 181 in session.hpp.  
Right now it's set to 3 seconds. if you double that you may get  
faster accelerating download speeds.

> b) Downloads between two peers won't go faster than 1Mb/s  - is it  
> a limitation built into the library ?

I presume you mean 1 MB/s, that is also the download speed I get at  
most. Slightly about 1 MB/s, but that's the hard limit on my internet  
connection as well.

> Is it possible to override it (set_download_rate_limit doesn't seem  
> to help) ?

It's not an intentional limitation at least. I'm not sure what could  
be causing this. You don't think it may be your drive that is the  
bottleneck? I mean, with random seeks things could get pretty slow.

Maybe it's the download buffer size. Are you testing on a LAN with  
one other peer? trying to push the speed for a single connection?

I should probably take a look at such a setting trying to tweak it.

thanks.


--
Arvid Norberg




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