Re: [Vserver] scheduler: CPU_Scheduler paper vs CONFIG_VSERVER_HARDCPU

From: Herbert Poetzl <herbert_at_13thfloor.at>
Date: Thu 01 Mar 2007 - 17:40:33 GMT
Message-ID: <20070301174033.GA15791@MAIL.13thfloor.at>

On Wed, Feb 28, 2007 at 09:29:49AM -0800, Alex Shultz wrote:
> Hi list.
>
> I'm a newbie in VServer. And I'm a little bit confused
> about 'HARD LIMIT'. How 'hard limit' from
> http://linux-vserver.org/CPU_Scheduler and other docs
> intersects with CONFIG_VSERVER_HARDCPU kernel option?
>
> Is it the same thing or different?

the Token Bucket Scheduler Extension is enabled by
the CONFIG_VSERVER_HARDCPU option. the TB can be
used for several things, e.g. accounting, priorization
and of course to do hard limits and fair scheduling

> For example, I'd like to know, how CPU time will be
> distributed between two VServers with 3 identical busy
> loop's ( while (1) ) tasks:
>
> VServer 1 - one taks is running;
> VServer 2 - two taks are running;

with the TB Scheduler disabled, it will balance out
at 1:2 distributed over all CPUs, with the TB sched
enabled and priorization you will get something between
1:2 and 1:1 depending on your config, with the hard
limit or fair scheduling enabled, you can basically
get any ratio between those two, with or without
idle time on the host system

> I've take a look at the VServer
> patch-2.6.18.5-vs2.0.3-rc1.diff, and can't find the
> place where a task can be really held on (deactivated)
> when CONFIG_VSERVER_HARDCPU=n

that is correct ...

> So, I guess CPU time distribution will be:
>
> VServer 1 - 33%, VServer 2 - 66%. Am I wrong?

with CONFIG_VSERVER_HARDCPU=n, yes, as stated above

> The http://oldwiki.linux-vserver.org/vsched+explained
> paper says:
>
> "For simple cases, like evenly distributing cpu time
> between vservers, you probably just want to set the
> ratio to somewhere between 1/N (where N is the number
> of servers) and 1/P (where P is the maximum expected
> peak load per CPU), and not bother with hard
> scheduling."

> So, does it really mean that without
> CONFIG_VSERVER_HARDCPU, the cpu time will be "evenly
> distributed between __vservers__"? Is it correct?

no, and I cannot find the place where it would state
that any TB scheduling would happen with the TB scheduler
disabled :)

> If a task can be holded without
> CONFIG_VSERVER_HARDCPU, please, can you point me to
> the kernel source file and line?

sorry, doesn't happen, so I can't :)

HTC,
Herbert

> Please CC an answer to lxshltz@yahoo.com, I'm not
> subscribed to the list yet
>
>
>
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Received on Thu Mar 1 18:15:05 2007

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