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Subject: RE: [PATCH] (2/3) Initial load balancing
Date: Fri, 17 Jan 2003 10:49:06 -0800
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From: "Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com>
To: "Zwane Mwaikambo" <zwane@holomorphy.com>
Cc: "Martin J. Bligh" <mbligh@aracnet.com>,
       "Linus Torvalds" <torvalds@transmeta.com>,
       "linux-kernel" <linux-kernel@vger.kernel.org>
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> -----Original Message-----
> From: Zwane Mwaikambo [mailto:zwane@holomorphy.com] 
> Sent: Friday, January 17, 2003 10:42 AM
> To: Pallipadi, Venkatesh
> Cc: Martin J. Bligh; Linus Torvalds; linux-kernel
> Subject: RE: [PATCH] (2/3) Initial load balancing
> 
> 
> On Fri, 17 Jan 2003, Pallipadi, Venkatesh wrote:
> 
> > > +{
> > > +	unsigned long old_mask;
> > > +
> > > +	old_mask = p->cpus_allowed;
> > > +	if (!(old_mask & (1UL << dest_cpu)))
> > > +		return;
> > > +	/* force the process onto the specified CPU */
> > > +	set_cpus_allowed(p, 1UL << dest_cpu);
> > > +
> > > +	/* restore the cpus allowed mask */
> > > +	set_cpus_allowed(p, old_mask);
> > > +}
> > 
> > It may be better to add a _note_ to this function saying 
> that it is not
> > supposed to be called by multiple callers at the same time. 
> As of now, 
> > as it is called at exec time only, I think it is safe. But, 
> if it get used at other
> > places, (or called once+preempt) we may have situations 
> where we may loose the cpus_allowed mask
> > or miss some sched_migrate_task(). I am looking at, what if 
> some sched_migrate_task() 
> > or user set_affinity gets initiated in between two 
> set_cpus_allowed in
> > this routine. 
> 
> Shouldn't there be a get_task_struct there?
> 
> 	Zwane

Yes. A get_task_struct() and put_task_struct() there will make the whole

stuff in there lock-protected and should get rid of the issues I was
mentioning.

Thanks,
-Venkatesh
-
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