linux-kernel - Re: [PATCH v3] pseries: prevent free CPU ids to be reused on another node

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Message-ID: <955e0f2f-bd5b-1610-2dfc-6c0b8e94e295@linux.ibm.com>
Date:   Wed, 7 Apr 2021 17:00:38 +0200
From:   Laurent Dufour <ldufour@...ux.ibm.com>
To:     Nathan Lynch <nathanl@...ux.ibm.com>
Cc:     cheloha@...ux.ibm.com, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, mpe@...erman.id.au,
        benh@...nel.crashing.org, paulus@...ba.org
Subject: Re: [PATCH v3] pseries: prevent free CPU ids to be reused on another
 node

Le 07/04/2021 à 16:55, Nathan Lynch a écrit :
> Laurent Dufour <ldufour@...ux.ibm.com> writes:
>> Changes since V2, addressing Nathan's comments:
>>   - Remove the retry feature
>>   - Reduce the number of local variables (removing 'i')
> 
> I was more interested in not having two variables for NUMA nodes in the
> function named 'node' and 'nid', hoping at least one of them could have
> a more descriptive name. See below.
> 
>>   static int pseries_add_processor(struct device_node *np)
>>   {
>> -	unsigned int cpu;
>> +	unsigned int cpu, node;
>>   	cpumask_var_t candidate_mask, tmp;
>> -	int err = -ENOSPC, len, nthreads, i;
>> +	int err = -ENOSPC, len, nthreads, nid;
>>   	const __be32 *intserv;
>>   
>>   	intserv = of_get_property(np, "ibm,ppc-interrupt-server#s", &len);
>> @@ -163,9 +169,17 @@ static int pseries_add_processor(struct device_node *np)
>>   	zalloc_cpumask_var(&candidate_mask, GFP_KERNEL);
>>   	zalloc_cpumask_var(&tmp, GFP_KERNEL);
>>   
>> +	/*
>> +	 * Fetch from the DT nodes read by dlpar_configure_connector() the NUMA
>> +	 * node id the added CPU belongs to.
>> +	 */
>> +	nid = of_node_to_nid(np);
>> +	if (nid < 0 || !node_possible(nid))
>> +		nid = first_online_node;
>> +
>>   	nthreads = len / sizeof(u32);
>> -	for (i = 0; i < nthreads; i++)
>> -		cpumask_set_cpu(i, tmp);
>> +	for (cpu = 0; cpu < nthreads; cpu++)
>> +		cpumask_set_cpu(cpu, tmp);
>>   
>>   	cpu_maps_update_begin();
>>   
>> @@ -173,6 +187,19 @@ static int pseries_add_processor(struct device_node *np)
>>   
>>   	/* Get a bitmap of unoccupied slots. */
>>   	cpumask_xor(candidate_mask, cpu_possible_mask, cpu_present_mask);
>> +
>> +	/*
>> +	 * Remove free ids previously assigned on the other nodes. We can walk
>> +	 * only online nodes because once a node became online it is not turned
>> +	 * offlined back.
>> +	 */
>> +	for_each_online_node(node) {
>> +		if (node == nid) /* Keep our node's recorded ids */
>> +			continue;
>> +		cpumask_andnot(candidate_mask, candidate_mask,
>> +			       node_recorded_ids_map[node]);
>> +	}
>> +
> 
> e.g. change 'nid' to 'assigned_node' or similar, and I think this
> becomes easier to follow.

Fair enough, will send a v4

> Otherwise the patch looks fine to me now.
>