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From: Lauro Venancio <lvenanci@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, lwang@redhat.com, riel@redhat.com,
	Mike Galbraith <efault@gmx.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@kernel.org>
Subject: Re: [RFC 3/3] sched/topology: Different sched groups must not have the same balance cpu
Date: Mon, 17 Apr 2017 12:34:05 -0300
Message-ID: <731e0515-63e8-2a58-832d-89619065a328@redhat.com> (raw)
In-Reply-To: <20170414164909.tfybszncwkm4yxap@hirez.programming.kicks-ass.net>

On 04/14/2017 01:49 PM, Peter Zijlstra wrote:
> On Thu, Apr 13, 2017 at 10:56:09AM -0300, Lauro Ramos Venancio wrote:
>> Currently, the group balance cpu is the groups's first CPU. But with
>> overlapping groups, two different groups can have the same first CPU.
>>
>> This patch uses the group mask to mark all the CPUs that have a
>> particular group as its main sched group. The group balance cpu is the
>> first group CPU that is also in the mask.
> Please give a NUMA configuration and CPU number where this goes wrong.
On a 4 nodes with ring topology, the groups (0-1,3 [cpu 0]),  (0-2 [cpu
1]) and (0,2-3 [cpu 3]) share the same sched_group_capacity instance
when the first groups cpu is used to select the sgc.
>
> Because only the first group of a domain matters, and with the other
> thing fixed, I'm not immediately seeing where we go wobbly.

Before patch 2, the group balance cpu was implicitly used to select the
sched_group_capacity instance. When two different groups had the same
balance cpu, they shared the same sched_group_capacity instance.

After patch 2, one different sched_group_capacity instance is assigned
to each group instance.


This patch ensures tree things:

1) different instances of the same group share the same
sched_group_capacity instance.

2) instances of different groups don't share the same
sched_group_capacity instance.

3) the group balance cpu must be one of the cpus where the group is
installed.


I am rebasing this patch on top of your patches.

  reply index

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-13 13:56 [RFC 0/3] sched/topology: fix sched groups on NUMA machines with mesh topology Lauro Ramos Venancio
2017-04-13 13:56 ` [RFC 1/3] sched/topology: Refactor function build_overlap_sched_groups() Lauro Ramos Venancio
2017-04-13 14:50   ` Rik van Riel
2017-05-15  9:02   ` [tip:sched/core] " tip-bot for Lauro Ramos Venancio
2017-04-13 13:56 ` [RFC 2/3] sched/topology: fix sched groups on NUMA machines with mesh topology Lauro Ramos Venancio
2017-04-13 15:16   ` Rik van Riel
2017-04-13 15:48   ` Peter Zijlstra
2017-04-13 20:21     ` Lauro Venancio
2017-04-13 21:06       ` Lauro Venancio
2017-04-13 23:38         ` Rik van Riel
2017-04-14 10:48           ` Peter Zijlstra
2017-04-14 11:38   ` Peter Zijlstra
2017-04-14 12:20     ` Peter Zijlstra
2017-05-15  9:03       ` [tip:sched/core] sched/fair, cpumask: Export for_each_cpu_wrap() tip-bot for Peter Zijlstra
2017-05-17 10:53         ` hackbench vs select_idle_sibling; was: " Peter Zijlstra
2017-05-17 12:46           ` Matt Fleming
2017-05-17 14:49           ` Chris Mason
2017-05-19 15:00           ` Matt Fleming
2017-06-05 13:00             ` Matt Fleming
2017-06-06  9:21               ` Peter Zijlstra
2017-06-09 17:52                 ` Chris Mason
2017-06-08  9:22           ` [tip:sched/core] sched/core: Implement new approach to scale select_idle_cpu() tip-bot for Peter Zijlstra
2017-04-14 16:58     ` [RFC 2/3] sched/topology: fix sched groups on NUMA machines with mesh topology Peter Zijlstra
2017-04-17 14:40       ` Lauro Venancio
2017-04-13 13:56 ` [RFC 3/3] sched/topology: Different sched groups must not have the same balance cpu Lauro Ramos Venancio
2017-04-13 15:27   ` Rik van Riel
2017-04-14 16:49   ` Peter Zijlstra
2017-04-17 15:34     ` Lauro Venancio [this message]
2017-04-18 12:32       ` Peter Zijlstra

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