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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 2/3] sched/topology: fix sched groups on NUMA machines with mesh topology
Date: Mon, 17 Apr 2017 11:40:59 -0300
Message-ID: <c21ceced-400c-0986-e53f-4c5eea8b23dd@redhat.com> (raw)
In-Reply-To: <20170414165857.7n75lxk4usfsbjaq@hirez.programming.kicks-ass.net>

On 04/14/2017 01:58 PM, Peter Zijlstra wrote:
> On Fri, Apr 14, 2017 at 01:38:13PM +0200, Peter Zijlstra wrote:
>> On Thu, Apr 13, 2017 at 10:56:08AM -0300, Lauro Ramos Venancio wrote:
>>> This patch constructs the sched groups from each CPU perspective. So, on
>>> a 4 nodes machine with ring topology, while nodes 0 and 2 keep the same
>>> groups as before [(3, 0, 1)(1, 2, 3)], nodes 1 and 3 have new groups
>>> [(0, 1, 2)(2, 3, 0)]. This allows moving tasks between any node 2-hops
>>> apart.
>> Ah,.. so after drawing pictures I see what went wrong; duh :-(
>>
>> An equivalent patch would be (if for_each_cpu_wrap() were exposed):
>>
>> @@ -521,11 +588,11 @@ build_overlap_sched_groups(struct sched_domain *sd, int cpu)
>>  	struct cpumask *covered = sched_domains_tmpmask;
>>  	struct sd_data *sdd = sd->private;
>>  	struct sched_domain *sibling;
>> -	int i;
>> +	int i, wrap;
>>  
>>  	cpumask_clear(covered);
>>  
>> -	for_each_cpu(i, span) {
>> +	for_each_cpu_wrap(i, span, cpu, wrap) {
>>  		struct cpumask *sg_span;
>>  
>>  		if (cpumask_test_cpu(i, covered))
>>
>>
>> We need to start iterating at @cpu, not start at 0 every time.
>>
>>
> OK, please have a look here:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/log/?h=sched/core

Looks good, but please hold these patches while patch 3 is not applied.
Without it, the sched_group_capacity (sg->sgc) instance is not selected
correctly and we have an important performance regression in all NUMA
machines.

I will continue this discussion in the other thread.

  reply index

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-13 13:56 [RFC 0/3] " 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 [this message]
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
2017-04-18 12:32       ` Peter Zijlstra

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