linux-kernel - Re: [RFC PATCH] sched/topology: Introduce NUMA identity node sched domain

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Date:   Fri, 11 Aug 2017 12:58:22 +0700
From:   Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, mingo@...hat.com, bp@...e.de
Subject: Re: [RFC PATCH] sched/topology: Introduce NUMA identity node sched
 domain



On 8/11/17 11:57, Suravee Suthikulpanit wrote:
>
>>> [...]
>>> @@ -1445,9 +1448,24 @@ void sched_init_numa(void)
>>>          tl[i] = sched_domain_topology[i];
>>>
>>>      /*
>>> +     * Ignore the NUMA identity level if it has the same cpumask
>>> +     * as previous level. This is the case for:
>>> +     *   - System with last-level-cache (MC) sched domain span a NUMA node.
>>> +     *   - System with DIE sched domain span a NUMA node.
>>> +     *
>>> +     * Assume all NUMA nodes are identical, so only check node 0.
>>> +     */
>>> +    if (!cpumask_equal(sched_domains_numa_masks[0][0], tl[i-1].mask(0)))
>>> +        tl[i++] = (struct sched_domain_topology_level){
>>> +            .mask = sd_numa_mask,
>>> +            .numa_level = 0,
>>> +            SD_INIT_NAME(NODE)
>>> +        };
>>
>> So what you've forgotten to mention is that for those systems where the
>> LLC == NODE this now superfluous level gets removed by the degenerate
>> code. Have you verified that does the right thing?
>
> Let me check with that one and get back.

Actually, it is not removed by the degenerate code. That is what this logic is 
for. It checks for LCC == NODE or DIE == NODE before setting up the NODE sched 
level. I can update the comment. This has also been tested on system w/ LLC == NODE.

Thanks,
Suravee