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From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Nikunj A. Dadhania" <nikunj@linux.vnet.ibm.com>,
	mingo@elte.hu, linux-kernel@vger.kernel.org,
	vatsa@linux.vnet.ibm.com, bharata@linux.vnet.ibm.com,
	paulus <paulus@samba.org>
Subject: Re: [RFC PATCH 0/4] Gang scheduling in CFS
Date: Tue, 20 Dec 2011 09:10:46 +1100	[thread overview]
Message-ID: <1324332646.30454.19.camel@pasglop> (raw)
In-Reply-To: <1324309901.24621.14.camel@twins>

On Mon, 2011-12-19 at 16:51 +0100, Peter Zijlstra wrote:
> On Mon, 2011-12-19 at 14:03 +0530, Nikunj A. Dadhania wrote:
> > The following patches implements gang scheduling. These patches
> >     are *highly* experimental in nature and are not proposed for
> >     inclusion at this time.
> 
> Nor will they ever be, I've always strongly opposed the whole concept
> and I'm not about to change my mind. Gang scheduling is a scalability
> nightmare. 
> 
> >     Gang scheduling can be helpful in virtualization scenario. It will
> >     help in avoiding the lock-holder-preemption[1] problem and other
> >     benefits include improved lock-acquisition times. This feature
> >     will help address some limitations of KVM on Power
> 
> Use paravirt ticket locks or a pause-loop-filter like thing.
> 
> >     On Power, we have an interesting hardware restriction on guests
> >     running across SMT theads: on any single core, we can only run one
> >     mm context at any given time. 
> 
> OMFG are your hardware engineers insane?

No we can run separate mm contexts, but we can only run one -partition-
at a time. Sadly the host kernel is also a partition for the MMU so that
means that all 4 threads must be running the same guest and enter/exit
the guest at the same time.

> Anyway, I had a look at your patches and I don't see how could ever
> work. You gang-schedule cgroup entities, but there's no guarantee the
> load-balancer will have at least one task for each group on every cpu.

Cheers,
Ben.




  parent reply	other threads:[~2011-12-19 22:11 UTC|newest]

Thread overview: 95+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-12-19  8:33 [RFC PATCH 0/4] Gang scheduling in CFS Nikunj A. Dadhania
2011-12-19  8:34 ` [RFC PATCH 1/4] sched: Adding cpu.gang file to cpu cgroup Nikunj A. Dadhania
2011-12-19  8:34 ` [RFC PATCH 2/4] sched: Adding gang scheduling infrastrucure Nikunj A. Dadhania
2011-12-19 15:51   ` Peter Zijlstra
2011-12-19 16:51     ` Peter Zijlstra
2011-12-20  1:43       ` Nikunj A Dadhania
2011-12-20  1:39     ` Nikunj A Dadhania
2011-12-19  8:34 ` [RFC PATCH 3/4] sched: Gang using set_next_buddy Nikunj A. Dadhania
2011-12-19  8:35 ` [RFC PATCH 4/4] sched:Implement set_gang_buddy Nikunj A. Dadhania
2011-12-19 15:51   ` Peter Zijlstra
2011-12-20  1:43     ` Nikunj A Dadhania
2011-12-26  2:30     ` Nikunj A Dadhania
2011-12-19 11:23 ` [RFC PATCH 0/4] Gang scheduling in CFS Ingo Molnar
2011-12-19 11:44   ` Avi Kivity
2011-12-19 11:50     ` Nikunj A Dadhania
2011-12-19 11:59       ` Avi Kivity
2011-12-19 12:06         ` Nikunj A Dadhania
2011-12-19 12:50           ` Avi Kivity
2011-12-19 13:09             ` Nikunj A Dadhania
2011-12-19 11:45   ` Nikunj A Dadhania
2011-12-19 13:22     ` Nikunj A Dadhania
2011-12-19 16:28       ` Ingo Molnar
2011-12-21 10:39   ` Nikunj A Dadhania
2011-12-21 10:43     ` Avi Kivity
2011-12-23  3:20       ` Nikunj A Dadhania
2011-12-23 10:36         ` Ingo Molnar
2011-12-25 10:58           ` Avi Kivity
2011-12-25 15:45             ` Avi Kivity
2011-12-26  3:14             ` Nikunj A Dadhania
2011-12-26  9:05               ` Avi Kivity
2011-12-26 11:33                 ` Nikunj A Dadhania
2011-12-26 11:41                   ` Avi Kivity
2011-12-27  1:47                     ` Nikunj A Dadhania
2011-12-27  9:15                       ` Avi Kivity
2011-12-27 10:24                         ` Nikunj A Dadhania
2011-12-29 16:07                 ` Better qemu/kvm defaults (was Re: [RFC PATCH 0/4] Gang scheduling in CFS) Dor Laor
2011-12-29 16:07                   ` [Qemu-devel] " Dor Laor
2011-12-29 16:13                   ` Avi Kivity
2011-12-29 16:13                     ` [Qemu-devel] " Avi Kivity
2011-12-29 16:16                   ` Anthony Liguori
2011-12-29 16:16                     ` Anthony Liguori
2012-01-01 10:16                     ` Dor Laor
2012-01-01 10:16                       ` [Qemu-devel] " Dor Laor
2012-01-01 14:01                       ` Ronen Hod
2012-01-01 14:01                         ` Ronen Hod
2012-01-02  9:37                         ` Dor Laor
2012-01-02  9:37                           ` [Qemu-devel] " Dor Laor
2012-01-03 15:48                       ` Anthony Liguori
2012-01-03 15:48                         ` Anthony Liguori
2012-01-03 22:31                         ` Dor Laor
2012-01-03 22:31                           ` Dor Laor
2012-01-03 22:45                           ` Anthony Liguori
2012-01-03 22:45                             ` [Qemu-devel] " Anthony Liguori
2012-01-03 22:59                             ` Dor Laor
2012-01-03 22:59                               ` Dor Laor
2011-12-27  3:15               ` [RFC PATCH 0/4] Gang scheduling in CFS Nikunj A Dadhania
2011-12-27  9:17                 ` Avi Kivity
2011-12-27  9:44                   ` Nikunj A Dadhania
2011-12-27  9:51                     ` Avi Kivity
2011-12-27 10:10                       ` Nikunj A Dadhania
2011-12-27 10:34                         ` Avi Kivity
2011-12-27 10:43                           ` Nikunj A Dadhania
2011-12-27 10:53                             ` Avi Kivity
2011-12-30  9:51             ` Ingo Molnar
2011-12-30 10:10               ` Nikunj A Dadhania
2011-12-31  2:21                 ` Nikunj A Dadhania
2012-01-02  4:20                   ` Nikunj A Dadhania
2012-01-02  9:39                     ` Avi Kivity
2012-01-02 10:22                       ` Nikunj A Dadhania
2012-01-02  9:37                   ` Avi Kivity
2012-01-02 10:30                     ` Nikunj A Dadhania
2012-01-02 13:33                       ` Avi Kivity
2012-01-04 10:52                     ` Nikunj A Dadhania
2012-01-04 14:41                       ` Avi Kivity
2012-01-04 14:56                         ` Srivatsa Vaddagiri
2012-01-04 17:13                           ` Avi Kivity
2012-01-05  6:57                             ` Nikunj A Dadhania
2012-01-04 16:47                         ` Rik van Riel
2012-01-04 17:16                           ` Avi Kivity
2012-01-04 20:56                             ` Rik van Riel
2012-01-04 21:31                             ` Peter Zijlstra
2012-01-04 21:41                               ` Avi Kivity
2012-01-05  9:10                                 ` Ingo Molnar
2012-02-20  8:08                                   ` Nikunj A Dadhania
2012-02-20  8:14                                     ` Ingo Molnar
2012-02-20 10:51                                     ` Peter Zijlstra
2012-02-20 11:53                                       ` Nikunj A Dadhania
2012-02-20 12:02                                         ` Srivatsa Vaddagiri
2012-02-20 12:14                                           ` Peter Zijlstra
2012-01-05  2:10                         ` Nikunj A Dadhania
2011-12-19 15:51 ` Peter Zijlstra
2011-12-19 16:09   ` Alan Cox
2011-12-19 22:10   ` Benjamin Herrenschmidt [this message]
2011-12-20  1:56   ` Nikunj A Dadhania
2011-12-20  8:52   ` Jeremy Fitzhardinge

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