[[!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.