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fix disk io docs

This commit is contained in:
Arvid Norberg 2010-03-01 19:42:37 +00:00
parent 77c0fa5872
commit 753215f79b
1 changed files with 30 additions and 9 deletions
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39
docs/manual.rst
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@ -3694,7 +3694,16 @@ session_settings
bool use_read_cache;
bool explicit_read_cache;
int explicit_cache_interval;
bool disk_io_no_buffer;
enum io_buffer_mode_t
{
enable_os_cache = 0,
disable_os_cache_for_aligned_files = 1,
disable_os_cache = 2
};
int disk_io_write_mode;
int disk_io_read_mode;
std::pair<int, int> outgoing_ports;
char peer_tos;
@ -4041,14 +4050,26 @@ There is an affinity to pick pieces that are already in the cache, so that
subsequent refreshes only swaps in pieces that are rarer than whatever is in
the cache at the time.
``disk_io_no_buffer`` defaults to true. When set to true, files are preferred
to be opened in unbuffered mode. This helps the operating system from growing
its file cache indefinitely. Currently only files whose offset in the torrent
is page aligned are opened in unbuffered mode. A page is typically 4096 bytes
and since blocks in bittorrent are 16kB, any file that is aligned to a block
or piece will get the benefit of be opened in unbuffered mode. It is therefore
recommended to make the largest file in a torrent the first file (with offset 0)
or use pad files to align all files to piece boundries.
``disk_io_write_mode`` and ``disk_io_read_mode`` determines how files are
opened when they're in read only mode versus read and write mode. The options
are:
* enable_os_cache
This is the default and files are opened normally, with the OS caching
reads and writes.
* disable_os_cache_for_aligned_files
This will open files in unbuffered mode for files where every read and
write would be sector aligned. Using aligned disk offsets is a requirement
on some operating systems.
* disable_os_cache
This opens all files in unbuffered mode (if allowed by the operating system).
Linux and Windows, for instance, require disk offsets to be sector aligned,
and in those cases, this option is the same as ``disable_os_caches_for_aligned_files``.
One reason to disable caching is that it may help the operating system from growing
its file cache indefinitely. Since some OSes only allow aligned files to be opened
in unbuffered mode, It is recommended to make the largest file in a torrent the first
file (with offset 0) or use pad files to align all files to piece boundries.
``outgoing_ports``, if set to something other than (0, 0) is a range of ports
used to bind outgoing sockets to. This may be useful for users whose router