Re: [PATCH 1/2] powerpc/papr_scm: Fetch nvdimm performance stats from PHYP

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

Thanks for reviewing this patch Ira,

My responses below inline.

Ira Weiny <ira.weiny@intel.com> writes:

> On Mon, Jun 22, 2020 at 09:54:50AM +0530, Vaibhav Jain wrote:
>> Update papr_scm.c to query dimm performance statistics from PHYP via
>> H_SCM_PERFORMANCE_STATS hcall and export them to user-space as PAPR
>> specific NVDIMM attribute 'perf_stats' in sysfs. The patch also
>> provide a sysfs ABI documentation for the stats being reported and
>> their meanings.
>> 
>> During NVDIMM probe time in papr_scm_nvdimm_init() a special variant
>> of H_SCM_PERFORMANCE_STATS hcall is issued to check if collection of
>> performance statistics is supported or not. If successful then a PHYP
>> returns a maximum possible buffer length needed to read all
>> performance stats. This returned value is stored in a per-nvdimm
>> attribute 'len_stat_buffer'.
>> 
>> The layout of request buffer for reading NVDIMM performance stats from
>> PHYP is defined in 'struct papr_scm_perf_stats' and 'struct
>> papr_scm_perf_stat'. These structs are used in newly introduced
>> drc_pmem_query_stats() that issues the H_SCM_PERFORMANCE_STATS hcall.
>> 
>> The sysfs access function perf_stats_show() uses value
>> 'len_stat_buffer' to allocate a buffer large enough to hold all
>> possible NVDIMM performance stats and passes it to
>> drc_pmem_query_stats() to populate. Finally statistics reported in the
>> buffer are formatted into the sysfs access function output buffer.
>> 
>> Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
>> ---
>>  Documentation/ABI/testing/sysfs-bus-papr-pmem |  27 ++++
>>  arch/powerpc/platforms/pseries/papr_scm.c     | 139 ++++++++++++++++++
>>  2 files changed, 166 insertions(+)
>> 
>> diff --git a/Documentation/ABI/testing/sysfs-bus-papr-pmem b/Documentation/ABI/testing/sysfs-bus-papr-pmem
>> index 5b10d036a8d4..c1a67275c43f 100644
>> --- a/Documentation/ABI/testing/sysfs-bus-papr-pmem
>> +++ b/Documentation/ABI/testing/sysfs-bus-papr-pmem
>> @@ -25,3 +25,30 @@ Description:
>>  				  NVDIMM have been scrubbed.
>>  		* "locked"	: Indicating that NVDIMM contents cant
>>  				  be modified until next power cycle.
>> +
>> +What:		/sys/bus/nd/devices/nmemX/papr/perf_stats
>> +Date:		May, 2020
>> +KernelVersion:	v5.9
>> +Contact:	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>, linux-nvdimm@lists.01.org,
>> +Description:
>> +		(RO) Report various performance stats related to papr-scm NVDIMM
>> +		device.  Each stat is reported on a new line with each line
>> +		composed of a stat-identifier followed by it value. Below are
>> +		currently known dimm performance stats which are reported:
>> +
>> +		* "CtlResCt" : Controller Reset Count
>> +		* "CtlResTm" : Controller Reset Elapsed Time
>> +		* "PonSecs " : Power-on Seconds
>> +		* "MemLife " : Life Remaining
>> +		* "CritRscU" : Critical Resource Utilization
>> +		* "HostLCnt" : Host Load Count
>> +		* "HostSCnt" : Host Store Count
>> +		* "HostSDur" : Host Store Duration
>> +		* "HostLDur" : Host Load Duration
>> +		* "MedRCnt " : Media Read Count
>> +		* "MedWCnt " : Media Write Count
>> +		* "MedRDur " : Media Read Duration
>> +		* "MedWDur " : Media Write Duration
>> +		* "CchRHCnt" : Cache Read Hit Count
>> +		* "CchWHCnt" : Cache Write Hit Count
>> +		* "FastWCnt" : Fast Write Count
>> \ No newline at end of file
>> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
>> index 9c569078a09f..cb3f9acc325b 100644
>> --- a/arch/powerpc/platforms/pseries/papr_scm.c
>> +++ b/arch/powerpc/platforms/pseries/papr_scm.c
>> @@ -62,6 +62,24 @@
>>  				    PAPR_PMEM_HEALTH_FATAL |	\
>>  				    PAPR_PMEM_HEALTH_UNHEALTHY)
>>  
>> +#define PAPR_SCM_PERF_STATS_EYECATCHER __stringify(SCMSTATS)
>> +#define PAPR_SCM_PERF_STATS_VERSION 0x1
>> +
>> +/* Struct holding a single performance metric */
>> +struct papr_scm_perf_stat {
>> +	u8 statistic_id[8];
>> +	u64 statistic_value;
>> +};
>> +
>> +/* Struct exchanged between kernel and PHYP for fetching drc perf stats */
>> +struct papr_scm_perf_stats {
>> +	u8 eye_catcher[8];
>> +	u32 stats_version;		/* Should be 0x01 */
>                                                      ^^^^
> 				     PAPR_SCM_PERF_STATS_VERSION?
Sure. Will update in v2

>
>> +	u32 num_statistics;		/* Number of stats following */
>> +	/* zero or more performance matrics */
>> +	struct papr_scm_perf_stat scm_statistic[];
>> +} __packed;
>> +
>>  /* private struct associated with each region */
>>  struct papr_scm_priv {
>>  	struct platform_device *pdev;
>> @@ -89,6 +107,9 @@ struct papr_scm_priv {
>>  
>>  	/* Health information for the dimm */
>>  	u64 health_bitmap;
>> +
>> +	/* length of the stat buffer as expected by phyp */
>> +	size_t len_stat_buffer;
>>  };
>>  
>>  static int drc_pmem_bind(struct papr_scm_priv *p)
>> @@ -194,6 +215,75 @@ static int drc_pmem_query_n_bind(struct papr_scm_priv *p)
>>  	return drc_pmem_bind(p);
>>  }
>>  
>> +/*
>> + * Query the Dimm performance stats from PHYP and copy them (if returned) to
>> + * provided struct papr_scm_perf_stats instance 'stats' of 'size' in bytes.
>> + * The value of R4 is copied to 'out' if the pointer is provided.
>> + */
>> +static int drc_pmem_query_stats(struct papr_scm_priv *p,
>> +				struct papr_scm_perf_stats *buff_stats,
>> +				size_t size, unsigned int num_stats,
>> +				uint64_t *out)
>> +{
>> +	unsigned long ret[PLPAR_HCALL_BUFSIZE];
>> +	struct papr_scm_perf_stat *stats;
>> +	s64 rc, i;
>> +
>> +	/* Setup the out buffer */
>> +	if (buff_stats) {
>> +		memcpy(buff_stats->eye_catcher,
>> +		       PAPR_SCM_PERF_STATS_EYECATCHER, 8);
>> +		buff_stats->stats_version =
>> +			cpu_to_be32(PAPR_SCM_PERF_STATS_VERSION);
>> +		buff_stats->num_statistics =
>> +			cpu_to_be32(num_stats);
>> +	} else {
>> +		/* In case of no out buffer ignore the size */
>> +		size = 0;
>> +	}
>> +
>> +	/*
>> +	 * Do the HCALL asking PHYP for info and if R4 was requested
>> +	 * return its value in 'out' variable.
>> +	 */
>> +	rc = plpar_hcall(H_SCM_PERFORMANCE_STATS, ret, p->drc_index,
>> +			 virt_to_phys(buff_stats), size);
>
> You are calling virt_to_phys(NULL) here when called from
> papr_scm_nvdimm_init()!  That can't be right.
Thanks for cathing this. However if the 'size' is '0' the 'buff_stats'
address is ignored by the hypervisor hence this didnt get caught in my
tests. Though CONFIG_DEBUG_VIRTUAL would have caught it early.

>
>> +	if (out)
>> +		*out =  ret[0];
>> +
>> +	if (rc == H_PARTIAL) {
>> +		dev_err(&p->pdev->dev,
>> +			"Unknown performance stats, Err:0x%016lX\n", ret[0]);
>> +		return -ENOENT;
>> +	} else if (rc != H_SUCCESS) {
>> +		dev_err(&p->pdev->dev,
>> +			"Failed to query performance stats, Err:%lld\n", rc);
>> +		return -ENXIO;
>> +	}
>> +
>> +	/* Successfully fetched the requested stats from phyp */
>> +	if (size != 0) {
>> +		buff_stats->num_statistics =
>> +			be32_to_cpu(buff_stats->num_statistics);
>> +
>> +		/* Transform the stats buffer values from BE to cpu native */
>> +		for (i = 0, stats = buff_stats->scm_statistic;
>> +		     i < buff_stats->num_statistics; ++i) {
>> +			stats[i].statistic_value =
>> +				be64_to_cpu(stats[i].statistic_value);
>> +		}
>> +		dev_dbg(&p->pdev->dev,
>> +			"Performance stats returned %d stats\n",
>> +			buff_stats->num_statistics);
>> +	} else {
>> +		/* Handle case where stat buffer size was requested */
>> +		dev_dbg(&p->pdev->dev,
>> +			"Performance stats size %ld\n", ret[0]);
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>>  /*
>>   * Issue hcall to retrieve dimm health info and populate papr_scm_priv with the
>>   * health information.
>> @@ -631,6 +721,45 @@ static int papr_scm_ndctl(struct nvdimm_bus_descriptor *nd_desc,
>>  	return 0;
>>  }
>>  
>> +static ssize_t perf_stats_show(struct device *dev,
>> +			       struct device_attribute *attr, char *buf)
>> +{
>> +	int index, rc;
>> +	struct seq_buf s;
>> +	struct papr_scm_perf_stat *stat;
>> +	struct papr_scm_perf_stats *stats;
>> +	struct nvdimm *dimm = to_nvdimm(dev);
>> +	struct papr_scm_priv *p = nvdimm_provider_data(dimm);
>> +
>> +	if (!p->len_stat_buffer)
>> +		return -ENOENT;
>> +
>> +	/* Allocate the buffer for phyp where stats are written */
>> +	stats = kzalloc(p->len_stat_buffer, GFP_KERNEL);
>
> I'm concerned that this buffer does not seem to have anything to do with the
> 'num_stats' parameter passed to drc_pmem_query_stats().  Furthermore why is
> num_stats always 0 in those calls?
>
'num_stats == 0' is a special case of the hcall where PHYP returns all
the possible stats in the 'stats' buffer.

>> +	if (!stats)
>> +		return -ENOMEM;
>> +
>> +	/* Ask phyp to return all dimm perf stats */
>> +	rc = drc_pmem_query_stats(p, stats, p->len_stat_buffer, 0, NULL);
>> +	if (!rc) {
>> +		/*
>> +		 * Go through the returned output buffer and print stats and
>> +		 * values. Since statistic_id is essentially a char string of
>> +		 * 8 bytes, simply use the string format specifier to print it.
>> +		 */
>> +		seq_buf_init(&s, buf, PAGE_SIZE);
>> +		for (index = 0, stat = stats->scm_statistic;
>> +		     index < stats->num_statistics; ++index, ++stat) {
>> +			seq_buf_printf(&s, "%.8s = 0x%016llX\n",
>> +				       stat->statistic_id, stat->statistic_value);
>> +		}
>> +	}
>> +
>> +	kfree(stats);
>> +	return rc ? rc : seq_buf_used(&s);
>> +}
>> +DEVICE_ATTR_RO(perf_stats);
>> +
>>  static ssize_t flags_show(struct device *dev,
>>  			  struct device_attribute *attr, char *buf)
>>  {
>> @@ -676,6 +805,7 @@ DEVICE_ATTR_RO(flags);
>>  /* papr_scm specific dimm attributes */
>>  static struct attribute *papr_nd_attributes[] = {
>>  	&dev_attr_flags.attr,
>> +	&dev_attr_perf_stats.attr,
>>  	NULL,
>>  };
>>  
>> @@ -696,6 +826,7 @@ 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;
>> +	u64 stat_size;
>>  
>>  	p->bus_desc.ndctl = papr_scm_ndctl;
>>  	p->bus_desc.module = THIS_MODULE;
>> @@ -759,6 +890,14 @@ static int papr_scm_nvdimm_init(struct papr_scm_priv *p)
>>  		dev_info(dev, "Region registered with target node %d and online node %d",
>>  			 target_nid, online_nid);
>>  
>> +	/* Try retriving the stat buffer and see if its supported */
>> +	if (!drc_pmem_query_stats(p, NULL, 0, 0, &stat_size)) {
>> +		p->len_stat_buffer = (size_t)stat_size;
>> +		dev_dbg(&p->pdev->dev, "Max perf-stat size %lu-bytes\n",
>> +			p->len_stat_buffer);
>> +	} else {
>> +		dev_info(&p->pdev->dev, "Limited dimm stat info available\n");
>
> Do we really need this print?
nvdimm performance stats can be selectively turned on/off from the
hypervisor management console hence this info message is more like a
warning indicating that extended dimm stat info like 'fuel_gauge' is not
available.

>
> Ira
>
>> +	}
>>  	return 0;
>>  
>>  err:	nvdimm_bus_unregister(p->bus);
>> -- 
>> 2.26.2
>> _______________________________________________
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-- 
Cheers
~ Vaibhav
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