linux-kernel - Re: [PATCH] sched,topology: Update sched topology atomically

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Date:   Mon, 11 Apr 2022 09:22:13 +0100
From:   Valentin Schneider <vschneid@...hat.com>
To:     Huang Ying <ying.huang@...el.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, Huang Ying <ying.huang@...el.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Ingo Molnar <mingo@...hat.com>, Mel Gorman <mgorman@...e.de>,
        Rik van Riel <riel@...riel.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Subject: Re: [PATCH] sched,topology: Update sched topology atomically

On 08/04/22 17:52, Valentin Schneider wrote:
>> +	topology = rcu_dereference(sched_numa_topology);
>> +	for (i = 0; i < topology->nr_levels; i++) {
>> +		if (!topology->masks[i][j])
>
> If I got default_numa_topology right and it's meant to be static,
> sched_numa_topology->masks can still be NULL, but here this would be gated
> by nr_levels being 0... Did I get that right?
>

Being a file-global variable, that's already init'd-as-0, (I'll use
my longish break as an excuse for forgetting that one), but the rest still
applies.

>>                       break;
>> -		cpu = cpumask_any_and(cpus, masks[i][j]);
>> +		cpu = cpumask_any_and(cpus, topology->masks[i][j]);
>>               if (cpu < nr_cpu_ids) {
>>                       found = cpu;
>>                       break;
>>               }
>>       }
>> -unlock:
>>       rcu_read_unlock();
>>
>>       return found;
>> --
>> 2.30.2