#!/usr/bin/perl -w

=head1 NAME

niceload - slow down a program when the load average is above a certain limit

=head1 SYNOPSIS

B<niceload> [-v] [-h] [-n nice] [-I io] [-L load] [-M mem] [-N]
[-t time] [-s time|-f factor] ( command | -p PID )

=head1 DESCRIPTION

GNU B<niceload> will slow down a program when the load average (or
other system activity) is above a certain limit. When the limit is
reached the program will be suspended for some time. Then resumed
again for some time.  Then the load average is checked again and we
start over.

Instead of load average B<niceload> can also look at disk I/O, amount
of free memory, or swapping activity.

If the load is 3.00 then the default settings will run a program
like this:

run 1 second, suspend (3.00-1.00) seconds, run 1 second, suspend
(3.00-1.00) seconds, run 1 second, ...

=head1 OPTIONS

=over 9

=item B<-f> I<FACTOR>

=item B<--factor> I<FACTOR>

Suspend time factor. Dynamically set B<-s> as amount over limit *
factor. Default is 1.


=item B<-H>

=item B<--hard>

Hard limit. B<--hard> will suspend the process until the system is
under the limits. The default is B<--soft>.


=item B<--io> I<iolimit>

=item B<-I> I<iolimit>

Limit for I/O. The amount of disk I/O will be computed as a value 0 -
10, where 0 is no I/O and 10 is at least one disk is 100% satuated.

B<--io> will set both B<--start-io> and B<run-io>.


=item B<--load> I<loadlimit>

=item B<-L> I<loadlimit>

Limit for load average.

B<--load> will set both B<--start-load> and B<run-load>.


=item B<--mem> I<memlimit>

=item B<-M> I<memlimit>

Limit for free memory. This is the amount of bytes available as free
+ cache. This limit is treated opposite other limits: If the system
is above the limit the program will run, if it is below the limit the
program will stop

I<memlimit> can be postfixed with K, M, G, T, or P which would
multiply the size with 1024, 1048576, 1073741824, or 1099511627776
respectively.

B<--mem> will set both B<--start-mem> and B<run-mem>.


=item B<--noswap>

=item B<-N>

No swapping. If the system is swapping both in and out it is a good
indication that the system is memory stressed.

B<--noswap> is over limit if the system is swapping both in and out.

B<--noswap> will set both B<--start-noswap> and B<run-noswap>.


=item B<-n> I<niceness>

=item B<--nice> I<niceness>

Sets niceness. See B<nice>(1).


=item B<-p> I<PID>

=item B<--pid> I<PID>

Process ID of process to suspend.


=item B<--quote>

=item B<-q>

Quote the command line. Useful if the command contains chars like *,
$, >, and " that should not be interpreted by the shell.


=item B<--run-io> I<iolimit>

=item B<--ri> I<iolimit>

=item B<--run-load> I<loadlimit>

=item B<--rl> I<loadlimit>

=item B<--run-mem> I<memlimit>

=item B<--rm> I<memlimit>

Run limit. The running program will be slowed down if the system is
above the limit. See: B<--io>, B<--load>, B<--mem>, B<--noswap>.


=item B<--start-io> I<iolimit>

=item B<--si> I<iolimit>

=item B<--start-load> I<loadlimit>

=item B<--sl> I<loadlimit>

=item B<--start-mem> I<memlimit>

=item B<--sm> I<memlimit>

Start limit. The program will not start until the system is below the
limit. See: B<--io>, B<--load>, B<--mem>, B<--noswap>.


=item B<--soft>

=item B<-S>

Soft limit. B<niceload> will suspend a process for a while and then
let it run for a second thus only slowing down a process while the
system is over one of the given limits. This is the default.


=item B<--suspend> I<SEC>

=item B<-s> I<SEC>

Suspend time. Suspend the command this many seconds when the max load
average is reached.


=item B<--recheck> I<SEC>

=item B<-t> I<SEC>

Recheck load time. Sleep SEC seconds before checking load
again. Default is 1 second.


=item B<--verbose>

=item B<-v>

Verbose. Print some extra output on what is happening. Use B<-v> until
you know what your are doing.

=back

=head1 EXAMPLE: See niceload in action

In terminal 1 run: top

In terminal 2 run:

B<niceload -q perl -e '$|=1;do{$l==$r or print "."; $l=$r}until(($r=time-$^T)>>B<50)'>

This will print a '.' every second for 50 seconds and eat a lot of
CPU. When the load rises to 1.0 the process is suspended.


=head1 EXAMPLE: Run updatedb

Running updatedb can often starve the system for disk I/O and thus result in a high load.

Run updatedb but suspend updatedb if the load is above 2.00:

B<niceload -L 2 updatedb>


=head1 EXAMPLE: Run rsync

rsync can just like updatedb starve the system for disk I/O and thus result in a high load.

Run rsync but keep load below 3.4. If load reaches 7 sleep for
(7-3.4)*12 seconds:

B<niceload -L 3.4 -f 12 rsync -Ha /home/ /backup/home/>


=head1 EXAMPLE: Ensure enough disk cache

Assume the program B<foo> uses 2 GB files intensively. B<foo> will run
fast if the files are in disk cache and be slow as a crawl if they are
not in the cache.

To ensure 2 GB are reserved for disk cache run:

B<niceload --hard --run-mem 2g foo>

This will not guarantee that the 2 GB memory will be used for the
files for B<foo>, but it will stop B<foo> if the memory for disk cache
is too low.


=head1 ENVIRONMENT VARIABLES

None. In future versions $NICELOAD will be able to contain default settings.

=head1 EXIT STATUS

Exit status should be the same as the command being run (untested).

=head1 REPORTING BUGS

Report bugs to <bug-parallel@gnu.org>.

=head1 AUTHOR

Copyright (C) 2004-11-19 Ole Tange, http://ole.tange.dk

Copyright (C) 2005,2006,2006,2008,2009,2010 Ole Tange, http://ole.tange.dk

Copyright (C) 2010,2011,2012 Ole Tange, http://ole.tange.dk and Free
Software Foundation, Inc.

=head1 LICENSE

Copyright (C) 2010,2011,2012 Free Software Foundation, Inc.

This program 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 3 of the License, or
at your option any later version.

This program 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.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.

=head2 Documentation license I

Permission is granted to copy, distribute and/or modify this documentation
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
Texts.  A copy of the license is included in the file fdl.txt.

=head2 Documentation license II

You are free:

=over 9

=item B<to Share>

to copy, distribute and transmit the work

=item B<to Remix>

to adapt the work

=back

Under the following conditions:

=over 9

=item B<Attribution>

You must attribute the work in the manner specified by the author or
licensor (but not in any way that suggests that they endorse you or
your use of the work).

=item B<Share Alike>

If you alter, transform, or build upon this work, you may distribute
the resulting work only under the same, similar or a compatible
license.

=back

With the understanding that:

=over 9

=item B<Waiver>

Any of the above conditions can be waived if you get permission from
the copyright holder.

=item B<Public Domain>

Where the work or any of its elements is in the public domain under
applicable law, that status is in no way affected by the license.

=item B<Other Rights>

In no way are any of the following rights affected by the license:

=over 2

=item *

Your fair dealing or fair use rights, or other applicable
copyright exceptions and limitations;

=item *

The author's moral rights;

=item *

Rights other persons may have either in the work itself or in
how the work is used, such as publicity or privacy rights.

=back

=back

=over 9

=item B<Notice>

For any reuse or distribution, you must make clear to others the
license terms of this work.

=back

A copy of the full license is included in the file as cc-by-sa.txt.

=head1 DEPENDENCIES

GNU B<niceload> uses Perl, and the Perl modules POSIX, and
Getopt::Long.

=head1 SEE ALSO

B<parallel>(1), B<nice>(1), B<uptime>(1)

=cut