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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
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>