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Running procs in VPS context :: possible to limit/throttle? [message #5163]

Wed, 16 August 2006 10:15

HaroldB
Messages: 61
Registered: June 2006

Member

Hello, the cpulimit resource does a fine job, but lets say a vps has 20 programs trying to run at once. They will use all of the cpulimit and beause they take longer to complete, the number of average running procs will be much higher than normal, which causes the hardware server's load to be higher.

So, it seems to me that cpulimit can hurt overal system performance under certain circumstances (more than a few concurrent, long-running processes per ve).

Is it possible to somehow limit the number of running procs in a ve? Am I missing something, like a simple workaround the problem stated above.

Thank you
Harold

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Re: Running procs in VPS context :: possible to limit/throttle? [message #5185 is a reply to message #5163]

Wed, 16 August 2006 15:07

dim
Messages: 344
Registered: August 2005

Senior Member

# man vzctl
# vzctl set VEID --numproc 80:80 --save

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Re: Running procs in VPS context :: possible to limit/throttle? [message #5186 is a reply to message #5163]

Wed, 16 August 2006 15:09

scythe
Messages: 22
Registered: December 2005
Location: Hungary

Junior Member

You mean --numproc parameter of vzctl?

EDIT: hehe, 2 seconds late, dim won Laughing

[Updated on: Wed, 16 August 2006 15:11]

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Re: Running procs in VPS context :: possible to limit/throttle? [message #5188 is a reply to message #5186]

Wed, 16 August 2006 15:14

HaroldB
Messages: 61
Registered: June 2006

Member

I am talking about running procs, not total procs.

total procs is useful but running procs can take down a system. Is it possible to limit running procs?

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Re: Running procs in VPS context :: possible to limit/throttle? [message #5189 is a reply to message #5188]

Wed, 16 August 2006 15:21

dim
Messages: 344
Registered: August 2005

Senior Member

I don't understand. There is only one task per CPU in the each moment, what do you mean? Number of tasks, which are ready to be executed for each VE? But how does it help?

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Re: Running procs in VPS context :: possible to limit/throttle? [message #5191 is a reply to message #5189]

Wed, 16 August 2006 15:23

HaroldB
Messages: 61
Registered: June 2006

Member

for example:

[root@server~]# vmstat
procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
5 2 6654616 38736 137608 1754916 0 2 1 0 1 0 16 10 59 15

5 running procs in this server. it has less than 5 cpus.

make sense now? how can we limit the number of running procs inside a vps.

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Re: Running procs in VPS context :: possible to limit/throttle? [message #5193 is a reply to message #5191]

Wed, 16 August 2006 15:26

dim
Messages: 344
Registered: August 2005

Senior Member

5 tasks with state RUNNING in scheduler queue.
It doesn't make sense to limit this queue.

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Re: Running procs in VPS context :: possible to limit/throttle? [message #5194 is a reply to message #5193]

Wed, 16 August 2006 15:28

HaroldB
Messages: 61
Registered: June 2006

Member

say a vps tries to run 100 concurrent processes... can openvz limit/throttle this?

like I said earlier, setting the cpulimit lower will only increase the number of running procs because they take longer to complete.

Do you agree on this point?

[Updated on: Wed, 16 August 2006 15:31]

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Re: Running procs in VPS context :: possible to limit/throttle? [message #5197 is a reply to message #5194]

Wed, 16 August 2006 15:35

dim
Messages: 344
Registered: August 2005

Senior Member

HaroldB wrote on Wed, 16 August 2006 11:28

say a vps tries to run 100 concurrent processes... can openvz handle/limit/throttle this?

like I said earlier, setting the cpulimit lower will only increase the number of running procs because they take longer to complete.

Do you agree on this point?

Agree.

There is cpuunits parameter also in OpenVZ. This parameter allow to set 'weight' of VE in respect of other VEs. If all VEs have equal weights, then one VE will have 1/number_of_ves CPU time no matter how much concurrent processes it runs. At the same time, if all VE's processes are in idle state, it's CPU time will be used by processes of other VEs.

Our scheduler operates in term of VEs, not processes.

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Re: Running procs in VPS context :: possible to limit/throttle? [message #5205 is a reply to message #5197]

Wed, 16 August 2006 16:19

HaroldB
Messages: 61
Registered: June 2006

Member

Thanks for the info, that makes sense. Here is my question another way.

Lets say a ve runs a program like "cpu-burn" (program which uses all avaialble cpu cycles) once. If that process stays running, it would add a load of 1 to the hardware node because its exactly one running process. However, if that program is run 50 times concurrently, a load of 50 is added. All the while, the same amount of cpu time is used by the vps. maybe this is an inherent part of an operating system, I am not sure.

it seems like an easy way to DOS a openvz/vz hn, by running tons of procs in the vps, even though your cpu usage is the same. I have tested this on vmware and the hardware node feels no effect, because of the seperate schedulers I believe.

[Updated on: Wed, 16 August 2006 16:22]

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Re: Running procs in VPS context :: possible to limit/throttle? [message #5221 is a reply to message #5163]

Wed, 16 August 2006 20:01

aistis
Messages: 77
Registered: September 2005
Location: Kaunas, Lithuania

Member

Harold, think for a second

cpulimit allows you to take care of CPU time the VE processes will get
cpuunits allows you to assign a priority for that CPU time the VE processes will get compared to other VEs (or in a words of dim)

now how you gonna DOS OVZ/VZ box? Are you afraid of tasks in the scheduler queue or what?

Aistis Zenkevicius

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Re: Running procs in VPS context :: possible to limit/throttle? [message #5227 is a reply to message #5205]

Wed, 16 August 2006 20:40

dev
Messages: 1693
Registered: September 2005
Location: Moscow

Senior Member

it is exactly the same for OVZ - we have 2-level CPU scheduer. On the first level VE to run is selected, on the second level a processes inside VE is selected.

So the first level CPU scheduler _limits_ and _makes_ sure that no VE can consume more CPU then it is allowed to. And VE is limited in CPU both due to cpulimits and its weight.

So what happens if you run 50 processes inside VE and 1 process on the node itself? Your loadavg on the node is 51 (/proc/loadavg or uptime output). But it has nothing to do with the _real_ load. It has nothing to do with the real load even on std Linux. It is just one of the parameters. And if your VE is limited to 10% of CPU these 50 processes won't be able to get more then 10% of CPU altogether. And the ONLY! process in host system will be able to consume 90% of CPU regardless of those 50.

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