linux-kernel - Re: [PATCH V9 1/2] powerpc/numa: Update CPU topology when VPHN enabled

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Message-Id: <98ae0ab7-5c46-c9a5-d927-109338fa8826@linux.vnet.ibm.com>
Date:   Wed, 23 Aug 2017 09:36:23 -0500
From:   Nathan Fontenot <nfont@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Michael Bringmann <mwb@...ux.vnet.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Cc:     John Allen <jallen@...ux.vnet.ibm.com>
Subject: Re: [PATCH V9 1/2] powerpc/numa: Update CPU topology when VPHN
 enabled

On 08/23/2017 06:41 AM, Michael Ellerman wrote:
> Michael Bringmann <mwb@...ux.vnet.ibm.com> writes:
> 
>> powerpc/numa: Correct the currently broken capability to set the
>> topology for shared CPUs in LPARs.  At boot time for shared CPU
>> lpars, the topology for each shared CPU is set to node zero, however,
>> this is now updated correctly using the Virtual Processor Home Node
>> (VPHN) capabilities information provided by the pHyp.
>>
>> Also, update initialization checks for device-tree attributes to
>> independently recognize PRRN or VPHN usage.
> 
> Did you ever do anything to address Nathan's comments on v4 ?
> 
>   http://patchwork.ozlabs.org/patch/767587/

Looking at this patch I do not see that VPHN is always enabled.

> 
> 
> Also your change log doesn't describe anything about what the patch does
> and why it is the correct fix for the problem.
> 
> When a DLPAR happens you modify the VPHN timer to run in 1 nsec, but you
> don't wait for it. Why would we not just run the logic synchronously?
> 
> It also seems to make VPHN and PRRN no longer exclusive, which looking
> at PAPR seems like it might be correct, but is also a major change so
> please justify it in detail.

This is correct, they are not exclusive. When we first added PRRN support
we mistakenly thought they were exclusive which is why the code currently
only starts PRRN, or VPHN if PRRN is not present.

> 
> Comments below.
> 
> 
>> diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
>> index b95c584..3fd4536 100644
>> --- a/arch/powerpc/mm/numa.c
>> +++ b/arch/powerpc/mm/numa.c
>> @@ -906,7 +907,7 @@ void __init initmem_init(void)
>>  
>>  	/*
>>  	 * Reduce the possible NUMA nodes to the online NUMA nodes,
>> -	 * since we do not support node hotplug. This ensures that  we
>> +	 * since we do not support node hotplug. This ensures that we
> 
> Please do whitespace/spelling changes in a separate patch.
> 
>>  	 * lower the maximum NUMA node ID to what is actually present.
>>  	 */
>>  	nodes_and(node_possible_map, node_possible_map, node_online_map);
>> @@ -1148,11 +1149,32 @@ struct topology_update_data {
>>  	int new_nid;
>>  };
>>  
>> +#define	TOPOLOGY_DEF_TIMER_SECS		60
>> +
>>  static u8 vphn_cpu_change_counts[NR_CPUS][MAX_DISTANCE_REF_POINTS];
>>  static cpumask_t cpu_associativity_changes_mask;
>>  static int vphn_enabled;
>>  static int prrn_enabled;
>>  static void reset_topology_timer(void);
>> +static int topology_timer_secs = TOPOLOGY_DEF_TIMER_SECS;
>> +static int topology_inited;
>> +static int topology_update_needed;
> 
> None of this code should be in numa.c. Which is not your fault but I'm
> inclined to move it before we make it worse.

Agreed. Perhaps this should all be in mm/vphn.c

-Nathan

> 
>> +
>> +/*
>> + * Change polling interval for associativity changes.
>> + */
>> +int timed_topology_update(int nsecs)
>> +{
>> +	if (nsecs > 0)
>> +		topology_timer_secs = nsecs;
>> +	else
>> +		topology_timer_secs = TOPOLOGY_DEF_TIMER_SECS;
>> +
>> +	if (vphn_enabled)
>> +		reset_topology_timer();
>> +
>> +	return 0;
>> +}
>>  
>>  /*
>>   * Store the current values of the associativity change counters in the
>> @@ -1246,6 +1268,12 @@ static long vphn_get_associativity(unsigned long cpu,
>>  			"hcall_vphn() experienced a hardware fault "
>>  			"preventing VPHN. Disabling polling...\n");
>>  		stop_topology_update();
>> +		break;
>> +	case H_SUCCESS:
>> +		printk(KERN_INFO
>> +			"VPHN hcall succeeded. Reset polling...\n");
> 
> We don't need that to hit everyone's console once a minute. Remove it or
> pr_debug() if you like.
> 
>> @@ -1363,6 +1394,8 @@ int numa_update_cpu_topology(bool cpus_locked)
>>  			cpumask_andnot(&cpu_associativity_changes_mask,
>>  					&cpu_associativity_changes_mask,
>>  					cpu_sibling_mask(cpu));
>> +			pr_info("Assoc chg gives same node %d for cpu%d\n",
>> +					new_nid, cpu);
> 
> No thanks.
> 
>> @@ -1379,6 +1412,9 @@ int numa_update_cpu_topology(bool cpus_locked)
>>  		cpu = cpu_last_thread_sibling(cpu);
>>  	}
>>  
>> +	if (i)
>> +		updates[i-1].next = NULL;
> 
> ???
> 
>> @@ -1453,6 +1490,14 @@ static void topology_schedule_update(void)
>>  	schedule_work(&topology_work);
>>  }
>>  
>> +void shared_topology_update(void)
>> +{
>> +	if (firmware_has_feature(FW_FEATURE_VPHN) &&
>> +		   lppaca_shared_proc(get_lppaca()))
>> +		topology_schedule_update();
>> +}
>> +EXPORT_SYMBOL(shared_topology_update);
> 
> There's no reason for that to be exported AFAICS.
> 
>> diff --git a/arch/powerpc/platforms/pseries/dlpar.c b/arch/powerpc/platforms/pseries/dlpar.c
>> index 3918769..ba9a4a0 100644
>> --- a/arch/powerpc/platforms/pseries/dlpar.c
>> +++ b/arch/powerpc/platforms/pseries/dlpar.c
>> @@ -592,6 +592,8 @@ static ssize_t dlpar_show(struct class *class, struct class_attribute *attr,
>>  
>>  static int __init pseries_dlpar_init(void)
>>  {
>> +	shared_topology_update();
>> +
> 
> I don't see any reason to call that from here.
> 
> It could just as easily be a machine init call in the file where it lives.
> 
> 
> cheers
>