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[[!meta title="I/O System"]]

[[!tag open_issue_hurd]]

The most obvious reason for the Hurd feeling slow compared to mainstream
systems like GNU/Linux, is a low I/O system performance, in particular very
slow hard disk access.

The reason for this slowness is lack and/or bad implementation of common
optimization techniques, like scheduling reads and writes to minimize head
movement; effective block caching; effective reads/writes to partial blocks;
reading/writing multiple blocks at once; and [[read-ahead]].  The
[[ext2_filesystem_server|hurd/translator/ext2fs]] might also need some
optimizations at a higher logical level.

The goal of this project is to analyze the current situation, and implement/fix
various optimizations, to achieve significantly better disk performance. It
requires understanding the data flow through the various layers involved in
disk access on the Hurd ([[filesystem|hurd/virtual_file_system]],
[[pager|hurd/libpager]], driver), and general experience with
optimizing complex systems.  That said, the killing feature we are definitely
missing is the [[read-ahead]], and even a very simple implementation would bring
very big performance speedups.

Here are some real testcases:

  * [[binutils_ld_64ksec]];

  * running the Git testsuite which is mostly I/O bound;

  * use [[TopGit]] on a non-toy repository.


Possible mentors: Samuel Thibault (youpi)

Exercise: Look through all the code involved in disk I/O, and try something
easy to improve. It's quite likely though that you will find nothing obvious --
in this case, please contact us about a different exercise task.