cpufreq: intel_pstate: Add debugfs file stats

Add stats file in debugfs under driver's parent directory (pstate_snb) which counts the time in nsecs per requested P state and the number of times the specific state was requested.

The file presents the statistics per logical CPU in the following format. The time is displayed in msecs:

CPU0
P-state Time Count

      16     4882777     23632
      17       21210       174
      18      549781      3300
      19       51171       461
      20       35487       394
      21       18173       219
      22       13752       258
      23        6048       172
      24        7754       177
      25        4587       151
      26        5465       162
      27        1432        47
      28         863        54
      29        1448        50
      30        1030        47
      31        1472        62
      32        2221        68
      33        1869        60
      34        2140        70
      39       85446      3803

...

The file can be used for debugging but also for monitoring various system workloads.

Also, make the debugfs_parent local as we never remove the driver's debugfs files.

Signed-off-by Stratos Karafotis <[email protected]>

---
  drivers/cpufreq/intel_pstate.c | 80 +++++++++++++++++++++++++++++++++++++++++-
  1 file changed, 79 insertions(+), 1 deletion(-)

drivers/cpufreq/intel_pstate.c +79 -1

index 31e2ae5..3a49269 100644
@@ -86,6 +86,12 @@ struct _pid {
  	int32_t last_err;
  };
 
+struct pstate_stat {
+	int pstate;
+	u64 time;
+	u64 count;
+};
+
  struct cpudata {
  	int cpu;
 

@@ -99,6 +105,7 @@ struct cpudata {
  	u64	prev_aperf;
  	u64	prev_mperf;
  	struct sample sample;
+	struct pstate_stat *stats;
  };
 
  static struct cpudata **all_cpu_data;

@@ -256,9 +263,59 @@ static struct pid_param pid_files[] = {
  	{NULL, NULL}
  };
 
-static struct dentry *debugfs_parent;
+static inline unsigned int stats_state_index(struct cpudata *cpu, int pstate)
+{
+	if (pstate <= cpu->pstate.max_pstate)
+		return pstate - cpu->pstate.min_pstate;
+	else
+		return cpu->pstate.max_pstate - cpu->pstate.min_pstate + 1;
+}
+
+static int stats_debug_show(struct seq_file *m, void *unused)
+{
+	struct cpudata *cpu;
+	int i, j, cnt;
+
+	get_online_cpus();
+	for_each_online_cpu(i) {
+		if (all_cpu_data[i])
+			cpu = all_cpu_data[i];
+		else
+			continue;
+
+		seq_printf(m, "CPU%u\n", i);
+		seq_puts(m, "P-state        Time     Count\n");
+
+		cnt = cpu->pstate.max_pstate - cpu->pstate.min_pstate + 2;
+		for (j = 0; j < cnt; j++)
+			seq_printf(m, "%7u %11llu %9llu\n",
+				   cpu->stats[j].pstate,
+				   cpu->stats[j].time / USEC_PER_MSEC,
+				   cpu->stats[j].count);
+
+		seq_puts(m, "\n");
+	}
+	put_online_cpus();
+
+	return 0;
+}
+
+static int stats_debug_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, stats_debug_show, inode->i_private);
+}
+
+static const struct file_operations fops_stats_pstate = {
+	.open		= stats_debug_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+	.owner		= THIS_MODULE,
+};
+
  static void intel_pstate_debug_expose_params(void)
  {
+	struct dentry *debugfs_parent;
  	int i = 0;
 
  	debugfs_parent = debugfs_create_dir("pstate_snb", NULL);

@@ -270,6 +327,8 @@ static void intel_pstate_debug_expose_params(void)
  				&fops_pid_param);
  		i++;
  	}
+	debugfs_create_file("stats", S_IRUSR | S_IRGRP, debugfs_parent, NULL,
+			    &fops_stats_pstate);
  }
 
  /************************** debugfs end ************************/

@@ -610,6 +669,7 @@ static inline void intel_pstate_calc_scaled_busy(struct cpudata *cpu)
  	int32_t core_busy, max_pstate, current_pstate, sample_ratio;
  	u32 duration_us;
  	u32 sample_time;
+	unsigned int i;
 
  	core_busy = cpu->sample.core_pct_busy;
  	max_pstate = int_tofp(cpu->pstate.max_pstate);

@@ -626,6 +686,10 @@ static inline void intel_pstate_calc_scaled_busy(struct cpudata *cpu)
  	}
 
  	cpu->sample.busy_scaled = core_busy;
+
+	i = stats_state_index(cpu, cpu->pstate.current_pstate);
+	cpu->stats[i].time += duration_us;
+	cpu->stats[i].count++;
  }
 
  static inline void intel_pstate_adjust_busy_pstate(struct cpudata *cpu)

@@ -692,6 +756,7 @@ MODULE_DEVICE_TABLE(x86cpu, intel_pstate_cpu_ids);
  static int intel_pstate_init_cpu(unsigned int cpunum)
  {
  	struct cpudata *cpu;
+	unsigned int i, cnt;
 
  	all_cpu_data[cpunum] = kzalloc(sizeof(struct cpudata), GFP_KERNEL);
  	if (!all_cpu_data[cpunum])

@@ -701,6 +766,17 @@ static int intel_pstate_init_cpu(unsigned int cpunum)
 
  	intel_pstate_get_cpu_pstates(cpu);
 
+	/* cnt equals to number of p-states + 1 (for turbo p-state) */
+	cnt = cpu->pstate.max_pstate - cpu->pstate.min_pstate + 2;
+	cpu->stats = kzalloc(sizeof(*cpu->stats) * cnt, GFP_KERNEL);
+	if (!cpu->stats) {
+		kfree(all_cpu_data[cpunum]);
+		return -ENOMEM;
+	}
+	for (i = 0; i < cnt - 1; i++)
+		cpu->stats[i].pstate = cpu->pstate.min_pstate + i;
+	cpu->stats[cnt - 1].pstate = cpu->pstate.turbo_pstate;
+
  	cpu->cpu = cpunum;
 
  	init_timer_deferrable(&cpu->timer);

@@ -779,6 +855,7 @@ static void intel_pstate_stop_cpu(struct cpufreq_policy *policy)
 
  	del_timer_sync(&all_cpu_data[cpu_num]->timer);
  	intel_pstate_set_pstate(cpu, cpu->pstate.min_pstate);
+	kfree(all_cpu_data[cpu_num]->stats);
  	kfree(all_cpu_data[cpu_num]);
  	all_cpu_data[cpu_num] = NULL;
  }

@@ -980,6 +1057,7 @@ out:
  	for_each_online_cpu(cpu) {
  		if (all_cpu_data[cpu]) {
  			del_timer_sync(&all_cpu_data[cpu]->timer);
+			kfree(all_cpu_data[cpu]->stats);
  			kfree(all_cpu_data[cpu]);
  		}
  	}

Quoted 8 lines · Stratos Karafotis

Add stats file in debugfs under driver's parent directory (pstate_snb) which counts the time in nsecs per requested P state and the number of times the specific state was requested.

The file presents the statistics per logical CPU in the following format. The time is displayed in msecs:

NAK

This adds significantly to the memory footprint to gather information that is available by post processing the perf tracepoint information. The increase isn't horrible on single socket desktop processor machines but gets big with server class machines. One vendor I have talked to considers a machine with 1024 cpus to be a SMALL machine.

Quoted 10 lines · Dirk Brandewie

Quoted 8 lines · Stratos Karafotis

Add stats file in debugfs under driver's parent directory (pstate_snb) which counts the time in nsecs per requested P state and the number of times the specific state was requested.

The file presents the statistics per logical CPU in the following format. The time is displayed in msecs:

Quoted 8 lines

NAK

This adds significantly to the memory footprint to gather information that is available by post processing the perf tracepoint information. The increase isn't horrible on single socket desktop processor machines but gets big with server class machines. One vendor I have talked to considers a machine with 1024 cpus to be a SMALL machine.

If I am not wrong the sizeof pstate_stat is 20B. On my CPU with 20 P states, we need 400B per logical CPU (3200B total in my desktop) plus 64B for stats pointers.

In your example this would need about 400KB - 500KB? Is it too much for 1024 a CPUs system?

I think it's a useful piece of info that we can have it directly without post processing tracepoint.
Is it acceptable to conditionally compile it with a new CONFIG option?

Thanks,
Stratos

Quoted 20 lines · Stratos Karafotis

Quoted 10 lines · Dirk Brandewie

Quoted 8 lines · Stratos Karafotis

Add stats file in debugfs under driver's parent directory (pstate_snb) which counts the time in nsecs per requested P state and the number of times the specific state was requested.

The file presents the statistics per logical CPU in the following format. The time is displayed in msecs:

Quoted 8 lines

NAK

This adds significantly to the memory footprint to gather information that is available by post processing the perf tracepoint information. The increase isn't horrible on single socket desktop processor machines but gets big with server class machines. One vendor I have talked to considers a machine with 1024 cpus to be a SMALL machine.

Quoted 5 lines

If I am not wrong the sizeof pstate_stat is 20B. On my CPU with 20 P states, we need 400B per logical CPU (3200B total in my desktop) plus 64B for stats pointers.

In your example this would need about 400KB - 500KB? Is it too much for 1024 a CPUs system?

For something that will likely not be used IMO yes.

Quoted 4 lines

I think it's a useful piece of info that we can have it directly without post processing tracepoint.
Is it acceptable to conditionally compile it with a new CONFIG option?

I can see where the information could be useful but the set of people that would find it useful is very small. Having information about residency since boot is interesting but just barely. This file will encourage people to build tools/scripts that rely on this file and they will complain bitterly if/when it changes or goes away so you would be creating a defacto ABI in debugfs.

This functionality will *not* be supportable in up coming processors where HWP is being used. See section 14.4 of the current SDM vol. 3
http://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-system-programming-manual-325384.pdf