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From: Nishanth Aravamudan <nacc@linux.vnet.ibm.com>
To: David Rientjes <rientjes@google.com>
Cc: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>,
	a.p.zijlstra@chello.nl, mingo@kernel.org, pjt@google.com,
	paul@paulmenage.org, akpm@linux-foundation.org, rjw@sisk.pl,
	nacc@us.ibm.com, paulmck@linux.vnet.ibm.com, tglx@linutronix.de,
	seto.hidetoshi@jp.fujitsu.com, tj@kernel.org,
	mschmidt@redhat.com, berrange@redhat.com,
	nikunj@linux.vnet.ibm.com, vatsa@linux.vnet.ibm.com,
	liuj97@gmail.com, linux-kernel@vger.kernel.org,
	linux-pm@vger.kernel.org
Subject: Re: [PATCH v3 5/5] cpusets, suspend: Save and restore cpusets during suspend/resume
Date: Mon, 14 May 2012 18:40:42 -0700	[thread overview]
Message-ID: <20120515014042.GA9774@linux.vnet.ibm.com> (raw)
In-Reply-To: <alpine.DEB.2.00.1205141735050.25235@chino.kir.corp.google.com>

On 14.05.2012 [17:37:50 -0700], David Rientjes wrote:
> On Mon, 14 May 2012, Srivatsa S. Bhat wrote:
> 
> > diff --git a/kernel/cpuset.c b/kernel/cpuset.c
> > index 0723183..671bf26 100644
> > --- a/kernel/cpuset.c
> > +++ b/kernel/cpuset.c
> > @@ -93,6 +93,13 @@ struct cpuset {
> >  
> >  	unsigned long flags;		/* "unsigned long" so bitops work */
> >  	cpumask_var_t cpus_allowed;	/* CPUs allowed to tasks in cpuset */
> > +
> > +	/*
> > +	 * used to save cpuset's cpus_allowed mask during suspend and restore
> > +	 * it during resume.
> > +	 */
> > +	cpumask_var_t suspend_cpus_allowed;
> > +
> >  	nodemask_t mems_allowed;	/* Memory Nodes allowed to tasks */
> >  
> >  	struct cpuset *parent;		/* my parent */
> 
> I see what you're doing with this and think it will fix the problem that 
> you're trying to address, but I think it could become much more general 
> to just the suspend case: if an admin sets a cpuset to have cpus 4-6, for 
> example, and cpu 5 goes offline, then I believe the cpuset should once 
> again become 4-6 if cpu 5 comes back online.  So I think this should be 
> implemented like mempolicies are which save the user intended nodemask 
> that may become restricted by cpuset placement but will be rebound if the 
> cpuset includes the intended nodes.

Heh, please read the thread at
http://marc.info/?l=linux-kernel&m=133615922717112&w=2 ... subject is
"[PATCH v2 0/7] CPU hotplug, cpusets: Fix issues with cpusets handling
upon CPU hotplug". That was effectively the same solution Srivatsa
originally posted. But after lengthy discussions with PeterZ and others,
it was decided that suspend/resume is a special case where it makes
sense to save "policy" but that generally cpu/memory hotplug is a
destructive operation and nothing is required to be retained (that
certain policies are retained is unfortunately now expected, but isn't
guaranteed for cpusets, at least).

> If that's done, then it takes care of the suspend case as well and adds 
> generic cpu hotplug support, not just for suspend/resume.

Yeah ... but that's not the intent here (to add generic cpu hotplug
support).

Srivatsa, perhaps a reference to some summary of why it's not good to
support the general hotplug case would have been good in 0/5?

Thanks,
Nish


-- 
Nishanth Aravamudan <nacc@us.ibm.com>
IBM Linux Technology Center


  reply	other threads:[~2012-05-15  1:40 UTC|newest]

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-05-13 23:14 [PATCH v3 0/5] CPU hotplug, cpusets: Fix issues with cpusets handling during suspend/resume Srivatsa S. Bhat
2012-05-13 23:15 ` [PATCH v3 1/5] cpusets, hotplug: Implement cpuset tree traversal in a helper function Srivatsa S. Bhat
2012-05-15  0:03   ` David Rientjes
2012-05-15 12:15     ` Srivatsa S. Bhat
2012-05-15 18:04       ` David Rientjes
2012-05-13 23:15 ` [PATCH v3 2/5] cpusets, hotplug: Restructure functions that are invoked during hotplug Srivatsa S. Bhat
2012-05-15  0:27   ` David Rientjes
2012-05-15 12:25     ` Srivatsa S. Bhat
2012-05-13 23:16 ` [PATCH v3 3/5] cpusets: Update tasks' cpus_allowed mask upon updates to root cpuset Srivatsa S. Bhat
2012-05-15  0:31   ` David Rientjes
2012-05-13 23:16 ` [PATCH v3 4/5] cpusets: Add provisions for distinguishing CPU Hotplug in suspend/resume path Srivatsa S. Bhat
2012-05-15  0:33   ` David Rientjes
2012-05-15 12:29     ` Srivatsa S. Bhat
2012-05-15 18:34       ` David Rientjes
2012-05-15 19:17         ` Srivatsa S. Bhat
2012-05-15 20:39           ` David Rientjes
2012-05-13 23:17 ` [PATCH v3 5/5] cpusets, suspend: Save and restore cpusets during suspend/resume Srivatsa S. Bhat
2012-05-15  0:37   ` David Rientjes
2012-05-15  1:40     ` Nishanth Aravamudan [this message]
2012-05-15  4:04       ` David Rientjes
2012-05-15  4:45         ` Nishanth Aravamudan
2012-05-15 18:31           ` David Rientjes
2012-05-15 20:10             ` Peter Zijlstra
2012-05-15 21:05               ` David Rientjes
2012-05-15 21:08                 ` Peter Zijlstra
2012-05-15 21:21                   ` Srivatsa S. Bhat
2012-05-15 21:24                     ` Peter Zijlstra
2012-05-15 21:24                   ` David Rientjes
2012-05-15 21:42                     ` Srivatsa S. Bhat
2012-05-15 21:49                       ` David Rientjes
2012-05-15 22:16                         ` Srivatsa S. Bhat
2012-05-15 22:32                           ` David Rientjes
2012-05-16  8:20                             ` Srivatsa S. Bhat
2012-05-16  8:42                               ` Srivatsa S. Bhat
2012-05-16 21:24                           ` Peter Zijlstra
2012-05-17  9:57                             ` Srivatsa S. Bhat
2012-05-15 21:13                 ` Peter Zijlstra
2012-05-15 21:37                   ` David Rientjes
2012-05-15  9:24       ` Srivatsa S. Bhat
2012-05-14 23:58 ` [PATCH v3 0/5] CPU hotplug, cpusets: Fix issues with cpusets handling " David Rientjes
2012-05-15 12:10   ` Srivatsa S. Bhat

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