delayacct: add delay max to record delay peak

Introduce the use cases of delay max, which can help quickly detect
potential abnormal delays in the system and record the types and specific
details of delay spikes.

Problem
========
Delay accounting can track the average delay of processes to show
system workload. However, when a process experiences a significant
delay, maybe a delay spike, which adversely affects performance,
getdelays can only display the average system delay over a period
of time. Yet, average delay is unhelpful for diagnosing delay peak.
It is not even possible to determine which type of delay has spiked,
as this information might be masked by the average delay.

Solution
=========
the 'delay max' can display delay peak since the system's startup,
which can record potential abnormal delays over time, including
the type of delay and the maximum delay. This is helpful for
quickly identifying crash caused by delay.

Use case
=========
bash# ./getdelays -d -p 244
print delayacct stats ON
PID     244

CPU             count     real total  virtual total    delay total  delay average      delay max
                   68      192000000      213676651         705643          0.010ms     0.306381ms
IO              count    delay total  delay average      delay max
                    0              0          0.000ms     0.000000ms
SWAP            count    delay total  delay average      delay max
                    0              0          0.000ms     0.000000ms
RECLAIM         count    delay total  delay average      delay max
                    0              0          0.000ms     0.000000ms
THRASHING       count    delay total  delay average      delay max
                    0              0          0.000ms     0.000000ms
COMPACT         count    delay total  delay average      delay max
                    0              0          0.000ms     0.000000ms
WPCOPY          count    delay total  delay average      delay max
                  235       15648284          0.067ms     0.263842ms
IRQ             count    delay total  delay average      delay max
                    0              0          0.000ms     0.000000ms

[wang.yaxin@zte.com.cn: update docs and fix some spelling errors]
  Link: https://lkml.kernel.org/r/20241213192700771XKZ8H30OtHSeziGqRVMs0@zte.com.cn
Link: https://lkml.kernel.org/r/20241203164848805CS62CQPQWG9GLdQj2_BxS@zte.com.cn
Co-developed-by: Wang Yong <wang.yong12@zte.com.cn>
Signed-off-by: Wang Yong <wang.yong12@zte.com.cn>
Co-developed-by: xu xin <xu.xin16@zte.com.cn>
Signed-off-by: xu xin <xu.xin16@zte.com.cn>
Co-developed-by: Wang Yaxin <wang.yaxin@zte.com.cn>
Signed-off-by: Wang Yaxin <wang.yaxin@zte.com.cn>
Signed-off-by: Kun Jiang <jiang.kun2@zte.com.cn>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Fan Yu <fan.yu9@zte.com.cn>
Cc: Peilin He <he.peilin@zte.com.cn>
Cc: tuqiang <tu.qiang35@zte.com.cn>
Cc: Yang Yang <yang.yang29@zte.com.cn>
Cc: ye xingchen <ye.xingchen@zte.com.cn>
Cc: Yunkai Zhang <zhang.yunkai@zte.com.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 21 insertions, 21 deletions

diff --git a/Documentation/accounting/delay-accounting.rst b/Documentation/accounting/delay-accounting.rst
index f61c01fc376e..8a0277428ccf 100644
--- a/Documentation/accounting/delay-accounting.rst
+++ b/Documentation/accounting/delay-accounting.rst
@@ -100,29 +100,29 @@ Get delays, since system boot, for pid 10::
 	# ./getdelays -d -p 10
 	(output similar to next case)
 
-Get sum of delays, since system boot, for all pids with tgid 5::
+Get sum and peak of delays, since system boot, for all pids with tgid 242::
 
-	# ./getdelays -d -t 5
+	bash-4.4# ./getdelays -d -t 242
 	print delayacct stats ON
-	TGID	5
-
-
-	CPU             count     real total  virtual total    delay total  delay average
-	                    8        7000000        6872122        3382277          0.423ms
-	IO              count    delay total  delay average
-                   0              0          0.000ms
-	SWAP            count    delay total  delay average
-                       0              0          0.000ms
-	RECLAIM         count    delay total  delay average
-                   0              0          0.000ms
-	THRASHING       count    delay total  delay average
-                       0              0          0.000ms
-	COMPACT         count    delay total  delay average
-                       0              0          0.000ms
-	WPCOPY          count    delay total  delay average
-                       0              0          0.000ms
-	IRQ             count    delay total  delay average
-                       0              0          0.000ms
+	TGID    242
+
+
+	CPU         count     real total  virtual total    delay total  delay average      delay max
+	              239      296000000      307724885        1127792          0.005ms     0.238382ms
+	IO          count    delay total  delay average      delay max
+	                0              0          0.000ms     0.000000ms
+	SWAP        count    delay total  delay average      delay max
+	                0              0          0.000ms     0.000000ms
+	RECLAIM     count    delay total  delay average      delay max
+	                0              0          0.000ms     0.000000ms
+	THRASHING   count    delay total  delay average      delay max
+	                0              0          0.000ms     0.000000ms
+	COMPACT     count    delay total  delay average      delay max
+	                0              0          0.000ms     0.000000ms
+	WPCOPY      count    delay total  delay average      delay max
+	              230       19100476          0.083ms     0.383822ms
+	IRQ         count    delay total  delay average      delay max
+	                0              0          0.000ms     0.000000ms
 
 Get IO accounting for pid 1, it works only with -p::