diff options
Diffstat (limited to 'open_issues')
| -rw-r--r-- | open_issues/performance/io_system.mdwn | 10 | ||||
| -rw-r--r-- | open_issues/performance/io_system/read-ahead.mdwn | 48 |
2 files changed, 53 insertions, 5 deletions
diff --git a/open_issues/performance/io_system.mdwn b/open_issues/performance/io_system.mdwn index 0d41d3c7..dbf7012a 100644 --- a/open_issues/performance/io_system.mdwn +++ b/open_issues/performance/io_system.mdwn @@ -1,4 +1,4 @@ -[[!meta copyright="Copyright © 2008, 2009, 2010 Free Software Foundation, +[[!meta copyright="Copyright © 2008, 2009, 2010, 2011 Free Software Foundation, Inc."]] [[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable @@ -6,8 +6,8 @@ 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]]."]]"""]] +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] [[!meta title="I/O System"]] @@ -20,7 +20,7 @@ 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 +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. @@ -30,7 +30,7 @@ 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 +missing is the [[read-ahead]], and even a very simple implementation would bring very big performance speedups. Here are some real testcases: diff --git a/open_issues/performance/io_system/read-ahead.mdwn b/open_issues/performance/io_system/read-ahead.mdwn new file mode 100644 index 00000000..b3b139c7 --- /dev/null +++ b/open_issues/performance/io_system/read-ahead.mdwn @@ -0,0 +1,48 @@ +[[!meta copyright="Copyright © 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]]."]]"""]] + +[[!tag open_issue_gnumach open_issue_hurd]] + +IRC, #hurd, freenode, 2011-02-13: + + <etenil> youpi: Would libdiskfs/diskfs.h be in the right place to make + readahead functions? + <youpi> etenil: no, it'd rather be at the memory management layer, + i.e. mach, unfortunately + <youpi> because that's where you see the page faults + <etenil> youpi: Linux also provides a readahead() function for higher level + applications. I'll probably have to add the same thing in a place that's + higher level than mach + <youpi> well, that should just be hooked to the same common implementation + <etenil> the man page for readahead() also states that portable + applications should avoid it, but it could be benefic to have it for + portability + <youpi> it's not in posix indeed + +IRC, #hurd, freenode, 2011-02-14: + + <etenil> youpi: I've investigated prefetching (readahead) techniques. One + called DiskSeen seems really efficient. I can't tell yet if it's patented + etc. but I'll keep you informed + <youpi> don't bother with complicated techniques, even the most simple ones + will be plenty :) + <etenil> it's not complicated really + <youpi> the matter is more about how to plug it into mach + <etenil> ok + <youpi> then don't bother with potential pattents + <antrik> etenil: please take a look at the work KAM did for last year's + GSoC + <youpi> just use a trivial technique :) + <etenil> ok, i'll just go the easy way then + + <braunr> antrik: what was etenil referring to when talking about + prefetching ? + <braunr> oh, madvise() stuff + <braunr> i could help him with that |