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New file - basic documentation for the table () system call.

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1998-07-21  Martin Baulig  <martin@home-of-linux.org>

	* table.sgml: New file - basic documentation for the
	table () system call.
This commit is contained in:
Martin Baulig
1998-07-21 20:39:01 +00:00
committed by Martin Baulig
parent 65fbcf1ea3
commit a129a83c45
6 changed files with 395 additions and 22 deletions
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18
doc/.cvsignore
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*.shml
*.ced
.timestamp
.timestamp2
.timestamp3
dbtohtml-1.shtml
dbtohtml-2.shtml
dbtohtml-3.shtml
dbtohtml.shtml
.timestamp4
gnome-hackers
gnome-hackers.ced
libgtop
libgtop-1.shtml
libgtop-2.shtml
libgtop-3.shtml
libgtop-4.shtml
libgtop-5.shtml
libgtop-INDEX.shtml
libgtop-ref
libgtop-ref.ced
libgtop.ced
libgtop.fot
libgtop.shtml
table

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doc/ChangeLog Normal file
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1998-07-21 Martin Baulig <martin@home-of-linux.org>
* table.sgml: New file - basic documentation for the
table () system call.

29
doc/Makefile
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@@ -1,22 +1,37 @@
all: .timestamp .timestamp2 .timestamp3
all: .timestamp .timestamp2 .timestamp3 .timestamp4
clean:
-rm -f .timestamp*
-rm -rf libgtop gnome-hackers libgtop-ref table
.timestamp: libgtop.sgml
rm -rf libgtop
-rm -rf libgtop
mkdir libgtop
jade -D /usr/lib/sgml/jade_dsl -d libgtop.dsl -t sgml \
-rm -f .timestamp
jade -D /usr/lib/sgml -d libgtop.dsl -t sgml \
-V %no-make-index% libgtop.sgml > /dev/null && \
touch .timestamp
.timestamp2: gnome-hackers.sgml
rm -rf gnome-hackers
-rm -rf gnome-hackers
mkdir gnome-hackers
jade -D /usr/lib/sgml/jade_dsl -d gnome-hackers.dsl -t sgml \
-rm -f .timestamp2
jade -D /usr/lib/sgml -d gnome-hackers.dsl -t sgml \
-V %no-make-index% gnome-hackers.sgml > /dev/null && \
touch .timestamp2
.timestamp3: libgtop-ref.sgml ../guile/reference.sgml
rm -rf libgtop-ref
-rm -rf libgtop-ref
mkdir libgtop-ref
jade -D /usr/lib/sgml/jade_dsl -d libgtop-ref.dsl -t sgml \
-rm -f .timestamp3
jade -D /usr/lib/sgml -d libgtop-ref.dsl -t sgml \
-V %no-make-index% libgtop-ref.sgml > /dev/null && \
touch .timestamp3
.timestamp4: table.sgml
-rm -rf table
mkdir table
-rm -f .timestamp4
jade -D /usr/lib/sgml -d table.dsl -t sgml \
-V %no-make-index% table.sgml > /dev/null && \
touch .timestamp4

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doc/table.announce.txt Normal file
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Path: news.uni-stuttgart.de!fu-berlin.de!taurus.uni-trier.DE!baulig
From: Martin Baulig <baulig@merkur.uni-trier.de>
Newsgroups: comp.os.linux.development.system
Subject: RFC: New system call for /proc information ?
Date: 07 Jun 1998 20:22:47 +0200
Lines: 143
Sender: baulig@Taurus.uni-trier.de
Message-ID: <of7zpfprs08.fsf@Taurus.uni-trier.de>
NNTP-Posting-Host: taurus.uni-trier.de (136.199.14.201)
Mime-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Transfer-Encoding: 8bit
NNTP-Posting-User: baulig
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X-Newsreader: Gnus v5.6.11/XEmacs 20.3 - "Vatican City"
Xref: news.uni-stuttgart.de comp.os.linux.development.system:73539
[Posted to the Gnome Mailing List and to comp.os.linux.development.system]
Request for Comments:
====================
Should we have a new system call under Linux which fetches information
from the /proc filesytem similar to the table() function of DEC OSF/1 ?
The whole story:
===============
I am currently working on libgtop, a library that fetches information
from the proc filesystem for user processes. This library uses a suid
server on system where this is required. On Linux, the information are
fetched directly from the proc filesystem.
Now, I made some profilings (fetches 50000 times cpu, memory, swap,
uptime and loadavg):
Each sample counts as 0.01 seconds.
% cumulative self self total
time seconds seconds calls ns/call ns/call name
91.86 348.03 348.03 read
3.07 359.67 11.64 open
0.67 362.22 2.55 close
0.16 363.55 0.62 memset
0.16 364.14 0.59 __ipc
0.03 368.84 0.12 vsscanf (iovsscanf.c:31)
0.01 374.49 0.05 sscanf (sscanf.c:28)
0.00 378.71 0.01 semctl (semctl.c:32)
0.00 378.73 0.01 shmctl (shmctl.c:30)
granularity: each sample hit covers 4 byte(s) for 0.00% of 378.88 seconds
index % time self children called name
[1] 91.9 348.03 0.00 read [1]
-----------------------------------------------
[2] 3.1 11.64 0.00 open [2]
-----------------------------------------------
[3] 0.7 2.55 0.00 close [3]
-----------------------------------------------
[5] 0.2 0.62 0.00 memset [5]
-----------------------------------------------
[6] 0.2 0.59 0.00 __ipc [6]
-----------------------------------------------
[35] 0.0 0.12 0.00 vsscanf (iovsscanf.c:31) [35]
-----------------------------------------------
[96] 0.0 0.05 0.00 sscanf (sscanf.c:28) [96]
-----------------------------------------------
You see, it spends a lot of time in read() which is only used to read the
data from the files in /proc. Well, basically one can say that these
timings are not so bad, normally a process periodically fetches those
information say 10 times a seconds which makes 36000 invocations per
hour.
This will make a total of about 250 seconds per hour or on even say:
``a program fetching those information at a frequency of 10 will take
about 7 % of each hour just for reading files from /proc''.
Now look at timings of __ipc, they're about 350 times better 'cause this
is done using system calls.
So far so good, now look at how this is done on the DEC OSF/1 port of the
library (the following code is part of libgtop - GPL/LGPL):
CPU usage:
{
struct tbl_sysinfo sysinfo;
int ret;
ret = table (TBL_SYSINFO, 0, (char *) &sysinfo, 1,
sizeof (struct tbl_sysinfo));
buf->user = sysinfo.si_user;
buf->nice = sysinfo.si_nice;
buf->sys = sysinfo.si_sys;
buf->idle = sysinfo.si_idle;
}
Well, the table() command of DEC OSF/1 has may disadvantages, too - such
as requiring to be root to fetch any information about processes (well, for
each process that is not the current one).
But this works using system calls rather that reading and parsing files
and should be about as fast as getting the IPC information on Linux.
Under Linux, the current trend seems to be to move anything into the /proc
filesystem, but if you look at the timings, wouldn't it be better to also
implement a system call interface ?
Don't understand me wrong:
=========================
I *do not want* to *replace* the /proc filesystem - it's an excellent
idea to be able to fetch all information on the command line without
any program just a simple 'cat' - I want to *add* a *new* system call
to allow programmers to fetch those information faster that reading
from /proc.
To come to the point:
=====================
Is there any public interest in having a new system call under Linux
which can be used to fetch all information that are currently in the
/proc filesystem.
Basically, this system would be defined like this:
asmlinkage int
sys_table (int command, struct sysinfo_table *buf)
and be invoked like this:
#include <sys/table.h>
{
struct sysinfo_cpu cpu;
struct sysinfo_mem mem;
ret = table (TABLE_CPU, &cpu);
if (ret == -1) return; /* or invoke any error handler */
ret = table (TABLE_MEM, &mem);
if (ret == -1) return;
}
What do you think, folks. Should we have such a system call under Linux ?
I can do the implementation of this system call, but I want to have some
feedback first.
Martin
--
-----------------------------------------------------------------
Martin Baulig - Angewandte Mathematik - Universitaet Trier
baulig@castor.uni-trier.de, http://www.home-of-linux.com/
Key: 1024-bit key with ID C8178435 created 1997/01/24
ID: 67 C1 84 A0 47 F5 11 C5 5F 68 4C 84 99 05 C3 92
Finger me for public key or fetch finger.txt from the url above
------------------------------------------------------------------

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<!doctype style-sheet PUBLIC "-//James Clark//DTD DSSSL Style Sheet//EN" [
<!ENTITY dbtohtml.dsl SYSTEM "dbtohtml.dsl" CDATA DSSSL >
]>
<style-specification id="tabledbotohtml" use="dbtohtml">
(define %output-basename% "table")
(define %output-directory% "table")
</style-specification>
<external-specification id="dbtohtml" document="dbtohtml.dsl">

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<!-- $Id$ -->
<!doctype book PUBLIC "-//Davenport//DTD DocBook V3.0//EN" [
<!entity libgtopConf.sh SYSTEM "../libgtopConf.sh" >
<!entity home-of-linux "http://www.home-of-linux.org/">
<!entity table-announce-first "&home-of-linux;kernel/table/ANNOUNCE.FIRST">
<!entity table20-tgz "&home-of-linux;kernel/table/table20.tgz">
<!entity table21-tgz "&home-of-linux;kernel/table/table21.tgz">
<!entity news-c-o-l-d-s "comp.os.linux.development.system">
<!entity libgtop "<productname>libgtop</productname>">
<!entity table "<function>table ()</function>">
]>
<book>
<bookinfo>
<title>The &table; system call under Linux</title>
<authorgroup>
<author>
<firstname>Martin</firstname>
<surname>Baulig</surname>
<affiliation>
<address>
<email>martin@home-of-linux.org</email>
</address>
</affiliation>
</author>
</authorgroup>
<copyright>
<year>1998</year>
<holder>Martin Baulig</holder>
</copyright>
<legalnotice>
<para>
This documentation is free software; you can redistribute
it and/or modify it under the terms of the GNU General Public
License as published by the Free Software Foundation; either
version 2 of the License, or (at your option) any later
version.
<para>
This library is distributed in the hope that it will be
useful, but WITHOUT ANY WARRANTY; without even the implied
warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE. See the GNU General Public License for more
details.
<para>
You should have received a copy of the GNU General Public
License along with this program; if not, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
MA 02111-1307 USA
<para>
For more details see the file COPYING in the source
distribution of LibGTop.</para>
</legalnotice>
<abstract>
<para>
<literal>$Id$</literal>
<para>
Under <productname>Linux</productname>, reading from
<filename>/proc</filename> is somehow slow because the data
needs to be converted into a stringified representation from
the kernel and to be parsed from the application program to
get the original data back.
While doing the <productname>DEC OSF/1</productname> port of
&libgtop; I got the idea to add something similar to the &table;
function there to the Linux kernel.
This is what this document is about.
</abstract>
</bookinfo>
<toc></toc>
<chapter id="why-not-sysctl">
<title>Why not <function>sysctl</function>?</title>
<para>
Some weeks ago, I posted the initial proposal of the project to
<ulink url="news:&news-c-o-l-d-s;">&news-c-o-l-d-s;</ulink> with
Message-ID <literal>&lt;of7zpfprs08.fsf@Taurus.uni-trier.de&gt;</literal>.
<para>
You can also read this article at my site:
<itemizedlist>
<listitem><para>
<ulink url="&table-announce-first;">&table-announce-first;</ulink>
</itemizedlist>
<para>
Some people told me to include all the stuff into
<function>sysctl</function> instead of inventing a new system call.
<para>
Basically this is a good idea, but the main problem with
<function>sysctl</function> is that this should be applied to standard
kernels and not just as a short patch. Well, AFAIK something similar
is on the "wish list" for 2.2er kernels - but of cause it'll need some
time until we have a real replacement of the <filename>/proc</filename>
filesystem in <function>sysctl</function>.
<para>
If someone thinks that this absolutely should be included in
<function>sysctl</function>: think about some kind of interface,
discuss it with the kernel developers, ...
<chapter id="about-table">
<title>About the &table; function</title>
<para>
Using the &table; function will not affect any existing kernel
structures and can be done independent from kernel development.
<para>
So it can easily be used in &libgtop; until we have something
simliar in standard kernels.
<para>
If you want to use the &table; function in your own programs, be
aware that it is just intended to be some kind of quick solution
for &libgtop; until there's something better in standard kernels.
<chapter id="how-to-use">
<title>How to use the &table; function in &libgtop;</title>
<para>
The source code of the &table; function is distributed together with
&libgtop;. It can be found in the <filename>kernel/table20</filename>
directory for 2.0.xx kernels and in the <filename>kernel/table21</filename>
directory for 2.1.xx kernels.
<para>
You can also download it from my site:
<itemizedlist>
<listitem><para>
<ulink url="&table20-tgz;">&table20-tgz</ulink>
(for kernel 2.0.xx)
<listitem><para>
<ulink url="&table21-tgz;">&table21-tgz</ulink>
(for kernel 2.1.xx)
</itemizedlist>
<para>
Copy the contents of the appropriate directory to
<filename>/usr/src/linux/table</filename>, apply the
patch to the kernel and re-configure &libgtop;.
<para>
After that, you can unmount <filename>/proc</filename> and
&libgtop; will still work !
<note>
<para>
Maybe one could consider this as a bug, but currently there
isn't a configuration option to disable the &table; function
once you applied the patch ...
</note>
<note>
<para>
Currently I'm working on the 2.1.x version to implement some
features newer kernels have - so the 2.0.x version may not
have all features the 2.1.x one has.
</note>
<note>
<para>
The 2.1.x version of the &table; function is implemented
as a kernel module. You have to do a
<command>insmod table/module.o</command> manually to use it.
<para>
This has the advantage that you don't need to reboot if you
want to play around with the code a little bit.
</note>
</book>
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