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authorThomas Schwinge <thomas@schwinge.name>2011-02-14 17:08:47 +0100
committerThomas Schwinge <thomas@schwinge.name>2011-02-14 17:08:47 +0100
commit4d93ba7548629fff82aa03351132c85d478a8734 (patch)
tree0728298f96c2d90aef5da59cef7bb451704457cc
parent5b1145432bd23441a6ec28cc66410d679b1ebcef (diff)
open_issues/performance/io_system/read-ahead: New.
-rw-r--r--microkernel/mach/gnumach/projects.mdwn11
-rw-r--r--open_issues/performance/io_system.mdwn10
-rw-r--r--open_issues/performance/io_system/read-ahead.mdwn48
3 files changed, 59 insertions, 10 deletions
diff --git a/microkernel/mach/gnumach/projects.mdwn b/microkernel/mach/gnumach/projects.mdwn
index 47a2756..f4ef192 100644
--- a/microkernel/mach/gnumach/projects.mdwn
+++ b/microkernel/mach/gnumach/projects.mdwn
@@ -1,13 +1,13 @@
-[[!meta copyright="Copyright © 2005, 2006, 2007, 2008 Free Software Foundation,
-Inc."]]
+[[!meta copyright="Copyright © 2005, 2006, 2007, 2008, 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]]."]]"""]]
+is included in the section entitled [[GNU Free Documentation
+License|/fdl]]."]]"""]]
This page is a place to keep track of ideas about things that may be improved
in GNU Mach, so that it'll evolve to a reliable microkernel for The Hurd, both
@@ -58,7 +58,8 @@ so that no duplicate efforts end up.
* Improve the external pagers interface
- * Implement read-ahead (huge I/O improvements expected).
+ * Implement [[open_issues/performance/io_system/read-ahead]] (huge I/O
+ improvements expected).
* Making this interface synchronous should improve I/O performance
significantly, without (almost) any drawbacks (we also get some
diff --git a/open_issues/performance/io_system.mdwn b/open_issues/performance/io_system.mdwn
index 0d41d3c..dbf7012 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 0000000..b3b139c
--- /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