linux-kernel - Re: [PATCH 2/2] cpusets: update tasks' cpus_allowed and mems

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Message-ID: <alpine.DEB.1.10.0806041149560.21323@chino.kir.corp.google.com>
Date:	Wed, 4 Jun 2008 12:01:11 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Paul Jackson <pj@....com>
cc:	Paul Menage <menage@...gle.com>, miaox@...fujitsu.com,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] cpusets: update tasks' cpus_allowed and mems_allowed
 after CPU/NODE offline/online

On Wed, 4 Jun 2008, Paul Jackson wrote:

> Do we need a new PF_* flag for this?  Perhaps one can test for this
> by examining the currently available properties of tasks.  Would it
> be sufficient to look for kernel threads (NULL mm_struct) whose
> cpus_allowed is a strict subset of the online CPUs?
> 

That would only identify kthreads that have been created with a subsequent 
call to set_cpus_allowed() or kthread_bind().

The PF_CPU_BOUND change targets only the latter since there are kthreads, 
such as kstopmachine, that can continue to manipulate their cpus_allowed 
during their lifetime.

Other kthreads such as the scheduler migration thread and soft lockup 
watchdog thread, however, always stay bound to a single cpu by use of 
kthread_bind().  These are the tasks that get the PF_CPU_BOUND flag and 
cannot be rebound via set_cpus_allowed() because of their negative 
effects.

		David
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