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[[!meta copyright="Copyright © 2008, 2009, 2010, 2011 Free Software Foundation,
Inc."]]
[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable
id="license" text="Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License, Version 1.2 or
any later version published by the Free Software Foundation; with no Invariant
Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license
is included in the section entitled [[GNU Free Documentation
License|/fdl]]."]]"""]]
[[!meta title="Disk I/O Performance Tuning"]]
[[!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|open_issues/performance/io_system/clustered_page_faults]]; and
[[open_issues/performance/io_system/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 [[open_issues/performance/io_system/read-ahead]], and even a very simple implementation would bring
very big performance speedups.
Here are some real testcases:
* [[open_issues/performance/io_system/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.
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