linux-kernel - Re: cgroup, RT cpu balance question

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Message-ID: <49BE354C.3090506@cn.fujitsu.com>
Date:	Mon, 16 Mar 2009 19:17:32 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Rolando Martins <rolando.martins@...il.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: cgroup, RT cpu balance question

Rolando Martins wrote:
> Hi,
> I have one question regarding RT cpu balance using cgroup.
> 
> cgroup
> echo 1 > cpuset.sched_load_balance
> 
> cgroup/2
> echo 0 > cpuset.mems
> echo 0-2 > cpuset.cpus
> echo 450000 > cpu.rt_runtime_us
> 
> cgroup/3
> echo 0 > cpuset.mems
> echo 3 > cpuset.cpus
> echo 450000 > cpu.rt_runtime_us
> 
> 
> I have a small test that uses a loop to utilize 100% cpu (SCHED_FIFO).
> When I run 2 tests on cgroup/3, it only uses bandwidth from cpu 3
> (100%), the balancing isn't happening.
> As I use the SCHED_FIFO, the 2 processes run sequentially.
> 
> Is this the expected behavior? Shouldn't the domains balance the spare
> cpu bandwidth?
> 

Then what do you expect? You put the task into cgroup/3 in which the allowed
cpus are restricted to CPU3, so of cause the scheduler will never schedule
the task to run on other cpus.

Please refer to Documentation/cgroups/cpusets.txt for the usage of cpusets.
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