From: Peter Zijlstra <peterz@infradead.org>
To: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
Cc: 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, rob@landley.net, tj@kernel.org,
mschmidt@redhat.com, berrange@redhat.com,
nikunj@linux.vnet.ibm.com, vatsa@linux.vnet.ibm.com,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
linux-pm@vger.kernel.org
Subject: Re: [PATCH v2 0/7] CPU hotplug, cpusets: Fix issues with cpusets handling upon CPU hotplug
Date: Fri, 04 May 2012 22:28:01 +0200 [thread overview]
Message-ID: <1336163281.6509.69.camel@twins> (raw)
In-Reply-To: <1336162456.6509.63.camel@twins>
On Fri, 2012-05-04 at 22:14 +0200, Peter Zijlstra wrote:
> > Also, we need to fix this problem at the CPU Hotplug level itself, and
> > not just for the suspend/resume case. Because, we have had numerous bug
> > reports and people complaining about this issue, in various scenarios,
> > including those that didn't involve suspend/resume.
>
> NO, absolutely not and I will NAK any and all such nonsense. WTF is a
> cpuset worth if you can run on random other cpus?
Sorting your cpuset 'problem' isn't nowhere near enough to make hotplug
'safe'. unplug also destroys task_struct::cpus_allowed.
Try it:
# schedtool -a 2 $$
# grep Cpus_allowed /proc/self/status
Cpus_allowed: 000004
# echo 0 > /sys/devices/system/cpu/cpu2/online
# grep Cpus_allowed /proc/self/status
Cpus_allowed: ffffff
See, hotplug is destructive, it has to be, there's no saying the cpu
will every come back.
So mucking about trying to make cpusets non-destructive is pointless.
The real bug is people using hotplug (for all kinds of stupid stuff) and
expecting anything different.
next prev parent reply other threads:[~2012-05-04 20:29 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-04 19:17 [PATCH v2 0/7] CPU hotplug, cpusets: Fix issues with cpusets handling upon CPU hotplug Srivatsa S. Bhat
2012-05-04 19:17 ` [PATCH v2 1/7] cpusets, hotplug: Implement cpuset tree traversal in a helper function Srivatsa S. Bhat
2012-05-04 19:18 ` [PATCH v2 2/7] cpusets, hotplug: Restructure functions that are invoked during hotplug Srivatsa S. Bhat
2012-05-04 19:18 ` [PATCH v2 3/7] cpusets: Introduce 'user_cpus_allowed' and rework the semantics of 'cpus_allowed' Srivatsa S. Bhat
2012-05-04 19:19 ` [PATCH v2 4/7] CPU hotplug, cpusets: Workout hotplug handling for cpusets Srivatsa S. Bhat
2012-05-04 19:19 ` [PATCH v2 5/7] Docs, cpusets: Update the cpuset documentation Srivatsa S. Bhat
2012-05-04 22:28 ` Rob Landley
2012-05-04 19:20 ` [PATCH v2 6/7] cpusets: Optimize the implementation of guarantee_online_cpus() Srivatsa S. Bhat
2012-05-04 19:20 ` [PATCH v2 7/7] cpusets: Remove out-dated comment about cpuset_track_online_cpus Srivatsa S. Bhat
2012-05-04 19:24 ` [PATCH v2 0/7] CPU hotplug, cpusets: Fix issues with cpusets handling upon CPU hotplug Peter Zijlstra
2012-05-04 19:58 ` Srivatsa S. Bhat
2012-05-04 20:14 ` Peter Zijlstra
2012-05-04 20:28 ` Peter Zijlstra [this message]
2012-05-04 20:49 ` Nishanth Aravamudan
2012-05-04 21:01 ` Peter Zijlstra
2012-05-04 21:27 ` Nishanth Aravamudan
2012-05-04 21:32 ` Peter Zijlstra
2012-05-04 21:34 ` Peter Zijlstra
2012-05-04 21:57 ` Nishanth Aravamudan
2012-05-04 21:38 ` Peter Zijlstra
2012-05-04 20:46 ` Nishanth Aravamudan
2012-05-04 20:56 ` Peter Zijlstra
2012-05-04 21:30 ` Nishanth Aravamudan
2012-05-04 21:44 ` Peter Zijlstra
2012-05-05 15:24 ` Alan Stern
2012-05-05 17:44 ` Paul E. McKenney
2012-05-05 18:56 ` Rafael J. Wysocki
2012-05-08 13:07 ` Daniel P. Berrange
2012-05-05 4:39 ` Mike Galbraith
2012-05-05 17:15 ` Srivatsa S. Bhat
2012-05-07 15:26 ` Jiang Liu
2012-05-09 9:12 ` Srivatsa S. Bhat
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