iocost_monitor: Always use strings for json values

Json has limited accuracy for numbers and can silently truncate 64bit
values, which can be extremely confusing.  Let's consistently use
string encapsulated values for json output.

While at it, convert an unnecesary f-string to str().
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

tools/cgroup/iocost_monitor.py

@@ -111,14 +111,14 @@ class IocStat:
 
     def dict(self, now):
         return { 'device'               : devname,
-                 'timestamp'            : now,
-                 'enabled'              : self.enabled,
-                 'running'              : self.running,
-                 'period_ms'            : self.period_ms,
-                 'period_at'            : self.period_at,
-                 'period_vtime_at'      : self.vperiod_at,
-                 'busy_level'           : self.busy_level,
-                 'vrate_pct'            : self.vrate_pct, }
+                 'timestamp'            : str(now),
+                 'enabled'              : str(int(self.enabled)),
+                 'running'              : str(int(self.running)),
+                 'period_ms'            : str(self.period_ms),
+                 'period_at'            : str(self.period_at),
+                 'period_vtime_at'      : str(self.vperiod_at),
+                 'busy_level'           : str(self.busy_level),
+                 'vrate_pct'            : str(self.vrate_pct), }
 
     def table_preamble_str(self):
         state = ('RUN' if self.running else 'IDLE') if self.enabled else 'OFF'
@@ -171,19 +171,19 @@ class IocgStat:
 
     def dict(self, now, path):
         out = { 'cgroup'                : path,
-                'timestamp'             : now,
-                'is_active'             : self.is_active,
-                'weight'                : self.weight,
-                'weight_active'         : self.active,
-                'weight_inuse'          : self.inuse,
-                'hweight_active_pct'    : self.hwa_pct,
-                'hweight_inuse_pct'     : self.hwi_pct,
-                'inflight_pct'          : self.inflight_pct,
-                'use_delay'             : self.use_delay,
-                'delay_ms'              : self.delay_ms,
-                'usage_pct'             : self.usage }
+                'timestamp'             : str(now),
+                'is_active'             : str(int(self.is_active)),
+                'weight'                : str(self.weight),
+                'weight_active'         : str(self.active),
+                'weight_inuse'          : str(self.inuse),
+                'hweight_active_pct'    : str(self.hwa_pct),
+                'hweight_inuse_pct'     : str(self.hwi_pct),
+                'inflight_pct'          : str(self.inflight_pct),
+                'use_delay'             : str(self.use_delay),
+                'delay_ms'              : str(self.delay_ms),
+                'usage_pct'             : str(self.usage) }
         for i in range(len(self.usages)):
-            out[f'usage_pct_{i}'] = f'{self.usages[i]}'
+            out[f'usage_pct_{i}'] = str(self.usages[i])
         return out
 
     def table_row_str(self, path):