CPU-DR for Zones

In my last entry, I described how to change the memory configuration of a running zone.  The natural next question is of course, if that also works with CPUs that have been assigned to a zone.  The answer, of course, is "yes".

You might wonder why that would be necessary in the first place.  After all, there's the Fair Share Scheduler, that's extremely capable of managing zones' CPU usage.  However, there are reasons to assign dedicated CPU resources to zones, licensing is one, SLAs with specified CPU requirements another.  In such cases, you configure a fixed amount of CPUs (more precisely, strands) for a zone.  Being able to change this configuration on the fly then becomes desirable.  I'll show how to do that in this blog entry.

In general, there are two ways to assign exclusive CPUs to a zone.  The classic approach is by using a resource pool with an associated processor set.  One or more zones can then be bound to that pool.  The easier solution is to use the parameter "dedicated-cpu" directly when configuring the zone.  In this second case, Solaris will create a temporary pool to manage these resources.  So effectively, the implementation is the same in both cases.  Which makes it clear how to change the CPU configuration in both cases: By changing the pool.  If you do this in the classical approach, the change to the pool will be persistent.  If working with the temporary pool created for the zone, you will also need to change the zone's configuration if you want the change to survive a zone restart.

If you configured you zone with "dedicated-cpu", the temporary pool (and also the temporary processor set that goes along with it) will usually be called "SUNWtmp_<zonename>".   If not, you'll know the name of the pool...  In both cases, everything else is the same:

Let's assume a zone called orazone, currently configured with 1 CPU.  It's to be assigned a second CPU.  The current pool configuration is like this:
root@benjaminchen:~# pooladm                

system default
	string	system.comment 
	int	system.version 1
	boolean	system.bind-default true
	string	system.poold.objectives wt-load

	pool pool_default
		int	pool.sys_id 0
		boolean	pool.active true
		boolean	pool.default true
		int	pool.importance 1
		string	pool.comment 
		pset	pset_default

	pool SUNWtmp_orazone
		int	pool.sys_id 5
		boolean	pool.active true
		boolean	pool.default false
		int	pool.importance 1
		string	pool.comment 
		boolean	pool.temporary true
		pset	SUNWtmp_orazone

	pset pset_default
		int	pset.sys_id -1
		boolean	pset.default true
		uint	pset.min 1
		uint	pset.max 65536
		string	pset.units population
		uint	pset.load 687
		uint	pset.size 3
		string	pset.comment 

		cpu
			int	cpu.sys_id 1
			string	cpu.comment 
			string	cpu.status on-line

		cpu
			int	cpu.sys_id 3
			string	cpu.comment 
			string	cpu.status on-line

		cpu
			int	cpu.sys_id 2
			string	cpu.comment 
			string	cpu.status on-line

	pset SUNWtmp_orazone
		int	pset.sys_id 2
		boolean	pset.default false
		uint	pset.min 1
		uint	pset.max 1
		string	pset.units population
		uint	pset.load 478
		uint	pset.size 1
		string	pset.comment 
		boolean	pset.temporary true

		cpu
			int	cpu.sys_id 0
			string	cpu.comment 
			string	cpu.status on-line
As we can see in the definition of pset SUNWtmp_orazone, it has been assigned CPU #0.  To add another CPU to this pool, you'll need these two commands:
root@benjaminchen:~# poolcfg -dc 'modify pset SUNWtmp_orapset \
                     (uint pset.max=2)' 
root@benjaminchen:~# poolcfg -dc 'transfer to pset \
                     orapset (cpu 1)'

To remove that CPU from the pool again, use these:

root@benjaminchen:~# poolcfg -dc 'transfer to pset pset_default \
                     (cpu 1)'
root@benjaminchen:~# poolcfg -dc 'modify pset SUNWtmp_orapset \
                     (uint pset.max=1)' 

That's it.   If you've used "dedicated-cpu" for your zone's configuration, you'll need to change that before the next reboot.  If not, you'd have to use the pool name you assigned to the zone.

Further details:

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Neuigkeiten, Tipps und Wissenswertes rund um SPARC, CMT, Performance und ihre Analyse sowie Erfahrungen mit Solaris auf dem Server und dem Laptop.

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