Re: [PATCH v4 1/2] powerpc/papr_scm: Fetch nvdimm performance stats from PHYP

Aneesh Kumar K.V
2020-07-31T07:12:57Z

Vaibhav Jain <vaibhav@linux.ibm.com> writes:

> 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 'stat_buffer_len'.
>
> 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
> 'stat_buffer_len' 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>
> ---
> Changelog:
>
> v4:
> * Fixed a build issue with this patch by moving a hunk from second
> patch in series to this patch. [ Aneesh ]
>
> v3:
> * Updated drc_pmem_query_stats() to not require 'buff_size' and 'out'
> args to the function. Instead 'buff_size' is calculated from
> 'num_stats' and instead of populating 'R4' in arg 'out' the value is
> returned from the function in case 'R4' represents
> 'max-buffer-size'.
>
> Resend:
> None
>
> v2:
> * Updated 'struct papr_scm_perf_stats' and 'struct papr_scm_perf_stat'
> to use big-endian types. [ Aneesh ]
> * s/len_stat_buffer/stat_buffer_len/ [ Aneesh ]
> * s/statistics_id/stat_id/ , s/statistics_val/stat_val/ [ Aneesh ]
> * Conversion from Big endian to cpu endian happens later rather than
> just after its fetched from PHYP.
> * Changed a log statement to unambiguously report dimm performance
> stats are not available for the given nvdimm [ Ira ]
> * Restructed some code to handle error case first [ Ira ]
> ---
> Documentation/ABI/testing/sysfs-bus-papr-pmem | 27 ++++
> arch/powerpc/platforms/pseries/papr_scm.c | 150 ++++++++++++++++++
> 2 files changed, 177 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 3d1235a76ba9..f37f3f70007d 100644
> --- a/arch/powerpc/platforms/pseries/papr_scm.c
> +++ b/arch/powerpc/platforms/pseries/papr_scm.c
> @@ -64,6 +64,26 @@
> 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 stat_id[8];
> + __be64 stat_val;
> +} __packed;
> +
> +/* Struct exchanged between kernel and PHYP for fetching drc perf stats */
> +struct papr_scm_perf_stats {
> + u8 eye_catcher[8];
> + /* Should be PAPR_SCM_PERF_STATS_VERSION */
> + __be32 stats_version;
> + /* Number of stats following */
> + __be32 num_statistics;
> + /* 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;
> @@ -92,6 +112,9 @@ struct papr_scm_priv {
>
> /* Health information for the dimm */
> u64 health_bitmap;
> +
> + /* length of the stat buffer as expected by phyp */
> + size_t stat_buffer_len;
> };
>
> static LIST_HEAD(papr_nd_regions);
> @@ -200,6 +223,79 @@ 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' that can hold atleast
> + * (num_stats + header) bytes.
> + * - If buff_stats == NULL the return value is the size in byes of the buffer
> + * needed to hold all supported performance-statistics.
> + * - If buff_stats != NULL and num_stats == 0 then we copy all known
> + * performance-statistics to 'buff_stat' and expect to be large enough to
> + * hold them.
> + * - if buff_stats != NULL and num_stats > 0 then copy the requested
> + * performance-statistics to buff_stats.
> + */
> +static ssize_t drc_pmem_query_stats(struct papr_scm_priv *p,
> + struct papr_scm_perf_stats *buff_stats,
> + unsigned int num_stats)
> +{
> + unsigned long ret[PLPAR_HCALL_BUFSIZE];
> + size_t size;
> + s64 rc;
> +
> + /* 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);
> +
> + /*
> + * Calculate the buffer size based on num-stats provided
> + * or use the prefetched max buffer length
> + */
> + if (num_stats)
> + /* Calculate size from the num_stats */
> + size = sizeof(struct papr_scm_perf_stats) +
> + num_stats * sizeof(struct papr_scm_perf_stat);
> + else
> + size = p->stat_buffer_len;
> + } else {
> + /* In case of no out buffer ignore the size */
> + size = 0;
> + }
> +
> + /* Do the HCALL asking PHYP for info */
> + rc = plpar_hcall(H_SCM_PERFORMANCE_STATS, ret, p->drc_index,
> + buff_stats ? virt_to_phys(buff_stats) : 0,
> + size);
> +
> + /* Check if the error was due to an unknown stat-id */
> + 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 -EIO;
> +
> + } else if (!size) {
> + /* Handle case where stat buffer size was requested */
> + dev_dbg(&p->pdev->dev,
> + "Performance stats size %ld\n", ret[0]);
> + return ret[0];
> + }
> +
> + /* Successfully fetched the requested stats from phyp */
> + dev_dbg(&p->pdev->dev,
> + "Performance stats returned %d stats\n",
> + be32_to_cpu(buff_stats->num_statistics));
> + return 0;
> +}
> +
> /*
> * Issue hcall to retrieve dimm health info and populate papr_scm_priv with the
> * health information.
> @@ -637,6 +733,48 @@ 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->stat_buffer_len)
> + return -ENOENT;
> +
> + /* Allocate the buffer for phyp where stats are written */
> + stats = kzalloc(p->stat_buffer_len, GFP_KERNEL);
> + if (!stats)
> + return -ENOMEM;
> +
> + /* Ask phyp to return all dimm perf stats */
> + rc = drc_pmem_query_stats(p, stats, 0);
> + if (rc)
> + goto free_stats;

So we end up making a HCALL for each read of the sysfs file? You do
throttle that for PAPR_HEALTH hcall (flags sysfs file). Do we need to do
that here? If not should we make this CAP_SYS_ADMIN? You can possibly
add is_visible callback to papr group and then restrict this all to
CAP_SYS_ADMIN?

> + /*
> + * Go through the returned output buffer and print stats and
> + * values. Since stat_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 < be32_to_cpu(stats->num_statistics);
> + ++index, ++stat) {
> + seq_buf_printf(&s, "%.8s = 0x%016llX\n",
> + stat->stat_id,
> + be64_to_cpu(stat->stat_val));
> + }
> +
> +free_stats:
> + 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)
> {
> @@ -682,6 +820,7 @@ 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,
> };
>
> @@ -702,6 +841,7 @@ 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;
> + ssize_t stat_size;
>
> p->bus_desc.ndctl = papr_scm_ndctl;
> p->bus_desc.module = THIS_MODULE;
> @@ -769,6 +909,16 @@ 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);
> --
> 2.26.2