In this post I will talk about the use of unsigned (integral) types in C++, or perhaps more specifically the rationale for using them. In my experience, it is common to use unsigned types for any variable holding a value that cannot be negative. Say, the number of bytes in a buffer.
This post is a result of looking into a slow-start performance issue in uTP. Slow-start is a mechanism in TCP employed to discover the capacity of a link, before transitioning into the steady state regime of additive increase and multiplicative decrease. Slow start is employed on new connections and after time-outs (where the congestion window . . .
Many aspects of bittorrent requires maintaining an estimate of some kinds of samples. uTP keeps a running estimate of round-trip times for each connection. When streaming torrents, it is useful to keep an estimate of download time per piece (to know what a reasonable timeout is). This post takes a closer look at how to . . .
This article is an attempt to sum up a small number of generic rules that appear to be useful rules of thumb when creating high performing programs. It is structured by first establishing some fundamental causes of performance hits followed by their extensions. memory latency A significant source of performance degradation on modern computers is the . . .
Deciding how many outstanding requests to keep to peers typically is based on the bandwidth delay product, or a simplified model thereof. The bandwidth delay product is the bandwidth capacity of a link multiplied by the latency of the link. It represents the number of bytes that fit in the wire and buffers along the . . .
banning peers sending corrupt data Bittorrent lets you verify data you receive from the swarm against the SHA-1 hashes in the .torrent file. This enable clients to ban peers that sends data that fails the hash check, and thus cannot be trusted. However, the integrity checking can only be done at piece level. A piece . . .
The typical bittorrent client user interface shows you a list of all torrents loaded in the client. Some of these torrents may be stopped and inactive, some of them may be seeding, but not having any peers interested in the torrent, and some (obviously) downloading. The simple (and probably most common) way to update the . . .
The typical design of bittorrent clients is to run SHA-1 hashing of piece data as it’s being written to disk (typically in a disk thread). Doing this helps keeping a lot of things simple. The disk cache and the disk operations are all synchronous, including the SHA-1 hashing. Whenever the disk cache decides to flush . . .
One of the key algorithms in bittorrent is the rarest-first piece picker. It is vital to bittorrent’s performance that the piece picker fulfills both of these requirements: The rarest piece is picked (from the client’s point of view of the swarm) If two or more pieces have the same rarity, pick one of them at . . .