Sergey Aleynikov
and 1 contributors

NAME

BSD::Process::Affinity - Manipulate CPU affinities on FreeBSD

SYNOPSIS

        use BSD::Process::Affinity;
        BSD::Process::Affinity->get_process_mask()->set(0x2)->update();

VERSION INCOMPABILITY

Version 0.4 has API partly incompatible with previous releases. Here are differences:

  • Functional interface is removed, only OO is available now

  • Lighten API - no more Bit::Vector object manipulations

  • from_num method is renamed to set, but for one more release is available under it's old name.

DESCRIPTION

Ability to manage CPU affinities from userland was a long-awaited feature in FreeBSD, and it is finally available since 7.1 release. This module allows you to programmatically manipulate them from perl level.

FreeBSD gives you three levels of restricting CPUs for a single process/thread:

  • 'Root' sets - they are set either for a whole system (and containing all processors), or for a jail. You can get root set to see at which processors can your process theoretically run.

  • Effetive process set - each process is a member of some set (otherwise, it wouldnt't be able run at all, heh). Many processes can be members of a single set, so altering such set - you alter many processes. These sets are only for processes, not for threads - threads can only manipulate with anonymous masks, and has effective set of parent process.

  • Per-process and per-thread anonymous masks. Each process can get/set it's own (or not own at all) mask, restricting available processors. Manipulating these masks is recommended way in manpages for application developers, when you want to set affinity just for a single process.

Beware, when manipulating affinities, you may degrade performance instead of gaining it.

INTERFACE

To operate with this module, you should do three steps:

  • Fetch an Affinity object for interesting kernel object (either old or new one)

  • Update it's internal state (or just fetch it)

  • If required, write changes back to the kernel using update method.

Here is an example that makes current thread NOT to run on 2nd processor in system:

        use BSD::Process::Affinity;
        my $obj = BSD::Process::Affinity->get_thread_mask();
        $obj->set($obj->get() & ~0x2)->update();

Note the chainable ability of update.

Whenever any error occurs, this module croaks.

Get Affinity object

All these methods (except for clone) expects one parameter - an id of object you want to fetch affinity of. You can just ommit it - this means 'give data for the current process/thread/whatever'.

clone

Clones current process'es effective set, and makes current process member of just created set.

rootof_set

Gets 'root' set for a given set id.

rootof_pid

Gets 'root' set for a given process id.

current_set

Gets set content by given set id.

current_pid

Gets effetive set for a given process id.

get_thread_mask

Get anonymous mask for a given thread id (not perl's thread id, but a system thread id).

get_process_mask

Get anonymous mask for a given process id.

Processors' mask manipulation

Here are existing Affinity object methods.

update

        $affinity->update();

Writes back to kernel changes made in set content. Without this call, your changes does not affect anything.

assign

        $affinity->assign($pid);

Assigns set specifiyed in $affinity object to be an effective set for process $pid.

It is an error to apply this method to anonymous masks.

get_cpusetid

        my $n = $affinity->get_cpusetid();

Returns cpu set internal id - for usage with rootof_set/current_set. Returns zero for anonymous masks.

get

        my $value = $affinity->get();

Returns usigned integer representing current mask. Then you can perform any actions with it, and set it back using set method. Lowest (rightmost) bit represents CPU0, and so on.

set

        $affinity->set(0x5);  #run on CPU0 and CPU2

Loads mask represented by $mask into object. Note that you have to call update to save changes to kernel, that is not done automatically.

Mask is treated as an unsigned integer, so number of processor it can represent depends on OS arccitecture - 32 or 64 bits.

This method is chainable with update.

SEE ALSO

http://www.freebsd.org/cgi/man.cgi?query=cpuset_getaffinity

http://www.freebsd.org/cgi/man.cgi?query=cpuset

AUTHOR

Sergey Aleynikov <sergey.aleynikov@gmail.com>

LICENSE

Copyright (c) 2009, 2011 by Sergey Aleynikov. All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.