Re: [PATCH] powerpc/papr_scm: Make 'perf_stats' invisible if perf-stats unavailable

[Vaibhav Jain <vaibhav@linux.ibm.com>]

"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> writes:

> Vaibhav Jain <vaibhav@linux.ibm.com> writes:
>
>> In case performance stats for an nvdimm are not available, reading the
>> 'perf_stats' sysfs file returns an -ENOENT error. A better approach is
>> to make the 'perf_stats' file entirely invisible to indicate that
>> performance stats for an nvdimm are unavailable.
>>
>> So this patch updates 'papr_nd_attribute_group' to add a 'is_visible'
>> callback implemented as newly introduced 'papr_nd_attribute_visible()'
>> that returns an appropriate mode in case performance stats aren't
>> supported in a given nvdimm.
>>
>> Also the initialization of 'papr_scm_priv.stat_buffer_len' is moved
>> from papr_scm_nvdimm_init() to papr_scm_probe() so that it value is
>> available when 'papr_nd_attribute_visible()' is called during nvdimm
>> initialization.
>>
>> Fixes: 2d02bf835e57('powerpc/papr_scm: Fetch nvdimm performance stats from PHYP')
>> Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
>> ---
>>  arch/powerpc/platforms/pseries/papr_scm.c | 37 ++++++++++++++++-------
>>  1 file changed, 26 insertions(+), 11 deletions(-)
>>
>> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
>> index 12f1513f0fca..90f0af8fefe8 100644
>> --- a/arch/powerpc/platforms/pseries/papr_scm.c
>> +++ b/arch/powerpc/platforms/pseries/papr_scm.c
>> @@ -907,6 +907,20 @@ static ssize_t flags_show(struct device *dev,
>>  }
>>  DEVICE_ATTR_RO(flags);
>>  
>> +umode_t papr_nd_attribute_visible(struct kobject *kobj, struct attribute *attr,
>> +				  int n)
>> +{
>> +	struct device *dev = container_of(kobj, typeof(*dev), kobj);
>> +	struct nvdimm *nvdimm = to_nvdimm(dev);
>> +	struct papr_scm_priv *p = nvdimm_provider_data(nvdimm);
>> +
>> +	/* For if perf-stats not available remove perf_stats sysfs */
>> +	if (attr == &dev_attr_perf_stats.attr && p->stat_buffer_len == 0)
>> +		return 0;
>> +
>> +	return attr->mode;
>> +}
>> +
>>  /* papr_scm specific dimm attributes */
>>  static struct attribute *papr_nd_attributes[] = {
>>  	&dev_attr_flags.attr,
>> @@ -916,6 +930,7 @@ static struct attribute *papr_nd_attributes[] = {
>>  
>>  static struct attribute_group papr_nd_attribute_group = {
>>  	.name = "papr",
>> +	.is_visible = papr_nd_attribute_visible,
>>  	.attrs = papr_nd_attributes,
>>  };
>>  
>> @@ -931,7 +946,6 @@ static int papr_scm_nvdimm_init(struct papr_scm_priv *p)
>>  	struct nd_region_desc ndr_desc;
>>  	unsigned long dimm_flags;
>>  	int target_nid, online_nid;
>> -	ssize_t stat_size;
>>  
>>  	p->bus_desc.ndctl = papr_scm_ndctl;
>>  	p->bus_desc.module = THIS_MODULE;
>> @@ -1016,16 +1030,6 @@ static int papr_scm_nvdimm_init(struct papr_scm_priv *p)
>>  	list_add_tail(&p->region_list, &papr_nd_regions);
>>  	mutex_unlock(&papr_ndr_lock);
>>  
>> -	/* Try retriving the stat buffer and see if its supported */
>> -	stat_size = drc_pmem_query_stats(p, NULL, 0);
>> -	if (stat_size > 0) {
>> -		p->stat_buffer_len = stat_size;
>> -		dev_dbg(&p->pdev->dev, "Max perf-stat size %lu-bytes\n",
>> -			p->stat_buffer_len);
>> -	} else {
>> -		dev_info(&p->pdev->dev, "Dimm performance stats unavailable\n");
>> -	}
>> -
>>  	return 0;
>>  
>>  err:	nvdimm_bus_unregister(p->bus);
>> @@ -1102,6 +1106,7 @@ static int papr_scm_probe(struct platform_device *pdev)
>>  	u64 blocks, block_size;
>>  	struct papr_scm_priv *p;
>>  	const char *uuid_str;
>> +	ssize_t stat_size;
>>  	u64 uuid[2];
>>  	int rc;
>>  
>> @@ -1179,6 +1184,16 @@ static int papr_scm_probe(struct platform_device *pdev)
>>  	p->res.name  = pdev->name;
>>  	p->res.flags = IORESOURCE_MEM;
>>  
>> +	/* Try retriving the stat buffer and see if its supported */
>> +	stat_size = drc_pmem_query_stats(p, NULL, 0);
>> +	if (stat_size > 0) {
>> +		p->stat_buffer_len = stat_size;
>> +		dev_dbg(&p->pdev->dev, "Max perf-stat size %lu-bytes\n",
>> +			p->stat_buffer_len);
>> +	} else {
>> +		dev_info(&p->pdev->dev, "Dimm performance stats unavailable\n");
>> +	}
>
> With this patch https://lore.kernel.org/linuxppc-dev/20210505191606.51666-1-vaibhav@linux.ibm.com
> We are adding details of whyy performance stat query hcall failed. Do we
> need to print again here?  Are we being more verbose here?
>
Yes agree this looks more verbose with the other patch you mentioned. I
have sent out a v2 of this patch with this dev_info removed.


> -aneesh
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-- 
Cheers
~ Vaibhav
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