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From: Rik van Riel <riel@redhat.com>
To: Avi Kivity <avi@redhat.com>
Cc: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>,
	Ingo Molnar <mingo@elte.hu>,
	peterz@infradead.org, linux-kernel@vger.kernel.org,
	vatsa@linux.vnet.ibm.com, bharata@linux.vnet.ibm.com
Subject: Re: [RFC PATCH 0/4] Gang scheduling in CFS
Date: Wed, 04 Jan 2012 15:56:49 -0500	[thread overview]
Message-ID: <4F04BD11.8090302@redhat.com> (raw)
In-Reply-To: <4F04898B.1080600@redhat.com>

On 01/04/2012 12:16 PM, Avi Kivity wrote:
> On 01/04/2012 06:47 PM, Rik van Riel wrote:
>>> So it looks like the default is optimal, at least wrt the cases you
>>> tested and your test workload.
>>
>>
>> It depends on the workload.
>>
>> I believe ebizzy synchronously bounces messages around between
>> userland threads, and may benefit from lower latency preemption
>> and re-scheduling.
>>
>> Workloads like AMQP do asynchronous messaging, and are likely
>> to benefit from having a lower number of switches.
>>
>> I do not know which kind of workload is more prevalent.
>>
>> Another worry with gang scheduling is scalability.  One of
>> the reasons Linux scales well to larger systems is that a
>> lot of things are done CPU local, without communicating
>> things with other CPUs.  Making the scheduling algorithm
>> system-global has the potential to add in a lot of overhead.
>>
>> Likewise, removing the ability to migrate workloads to idle
>> CPUs is likely to hurt a lot of real world workloads.
>>
>> Benchmarks don't care, because they run full-out. However,
>> users do not run benchmarks nearly as much as they run
>> actual workloads...
>>
>
> I think we can solve it at the guest level.  The paravirt ticketlock
> stuff introduces wait/wake calls (actually wait is just a HLT
> instruction); we could spin for a while, then HLT until the other side
> wakes us.  We should do this for all sites that busy wait.

Agreed, that would probably be the best (and nicest) solution.

-- 
All rights reversed

  reply	other threads:[~2012-01-04 20:57 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 [this message]
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
2011-12-20  1:56   ` Nikunj A Dadhania
2011-12-20  8:52   ` Jeremy Fitzhardinge

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