docs: update docs after introducing delaytop

The "getdelays" can only display the latency of a single task by
specifying a PID, we introduce the "delaytop" with the following
capabilities:

1. system view: monitors latency metrics (CPU, I/O, memory, IRQ, etc.)
   for all system processes

2. supports field-based sorting (e.g., default sort by CPU latency in
   descending order)

3. dynamic interactive interface: focus on specific processes with
   --pid; limit displayed entries with --processes 20; control monitoring
   duration with --iterations;

Link: https://lkml.kernel.org/r/2025071013514177028RdjISjqeIOnTCRvGAwy@zte.com.cn
Signed-off-by: Fan Yu <fan.yu9@zte.com.cn>
Signed-off-by: Wang Yaxin <wang.yaxin@zte.com.cn>
Signed-off-by: Jiang Kun <jiang.kun2@zte.com.cn>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Peilin He <he.peilin@zte.com.cn>
Cc: Qiang Tu <tu.qiang35@zte.com.cn>
Cc: wangyong <wang.yong12@zte.com.cn>
Cc: xu xin <xu.xin16@zte.com.cn>
Cc: Yang Yang <yang.yang29@zte.com.cn>
Cc: Yunkai Zhang <zhang.yunkai@zte.com.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/Documentation/accounting/delay-accounting.rst b/Documentation/accounting/delay-accounting.rst
index 210c194d4a7b5328a405e0ad706245fb9d0ab2fa..664950328fb70ad68e3fbdb5d12b23ff87f704b3 100644 (file)
--- a/Documentation/accounting/delay-accounting.rst
+++ b/Documentation/accounting/delay-accounting.rst
@@ -131,3 +131,50 @@ Get IO accounting for pid 1, it works only with -p::
        linuxrc: read=65536, write=0, cancelled_write=0
 
 The above command can be used with -v to get more debug information.
+
+After the system starts, use `delaytop` to get the Top-N high-latency tasks.
+this tool supports sorting by CPU latency in descending order by default,
+displays the top 20 high-latency tasks by default, and refreshes the latency
+data every 2 seconds by default.
+
+Get Top-N tasks delay, since system boot::
+
+       bash# ./delaytop
+       Top 20 processes (sorted by CPU delay):
+
+         PID   TGID  COMMAND            CPU(ms)  IO(ms)        SWAP(ms) RCL(ms) THR(ms)  CMP(ms)  WP(ms)  IRQ(ms)
+       ---------------------------------------------------------------------------------------------
+          32     32  kworker/2:0H-sy   23.65     0.00     0.00     0.00    0.00     0.00     0.00     0.00
+         497    497  kworker/R-scsi_    1.20     0.00     0.00     0.00    0.00     0.00     0.00     0.00
+         495    495  kworker/R-scsi_    1.13     0.00     0.00     0.00    0.00     0.00     0.00     0.00
+         494    494  scsi_eh_0          1.12     0.00     0.00     0.00    0.00     0.00     0.00     0.00
+         485    485  kworker/R-ata_s    0.90     0.00     0.00     0.00    0.00     0.00     0.00     0.00
+         574    574  kworker/R-kdmfl    0.36     0.00     0.00     0.00    0.00     0.00     0.00     0.00
+          34     34  idle_inject/3      0.33     0.00     0.00     0.00    0.00     0.00     0.00     0.00
+        1123   1123  nde-netfilter      0.28     0.00     0.00     0.00    0.00     0.00     0.00     0.00
+          60     60  ksoftirqd/7        0.25     0.00     0.00     0.00    0.00     0.00     0.00     0.00
+         114    114  kworker/0:2-cgr    0.25     0.00     0.00     0.00    0.00     0.00     0.00     0.00
+         496    496  scsi_eh_1          0.24     0.00     0.00     0.00    0.00     0.00     0.00     0.00
+          51     51  cpuhp/6            0.24     0.00     0.00     0.00    0.00     0.00     0.00     0.00
+        1667   1667  atd                0.24     0.00     0.00     0.00    0.00     0.00     0.00     0.00
+          45     45  cpuhp/5            0.23     0.00     0.00     0.00    0.00     0.00     0.00     0.00
+        1102   1102  nde-backupservi    0.22     0.00     0.00     0.00    0.00     0.00     0.00     0.00
+        1098   1098  systemsettings     0.21     0.00     0.00     0.00    0.00     0.00     0.00     0.00
+        1100   1100  audit-monitor      0.20     0.00     0.00     0.00    0.00     0.00     0.00     0.00
+          53     53  migration/6        0.20     0.00     0.00     0.00    0.00     0.00     0.00     0.00
+        1482   1482  sshd               0.19     0.00     0.00     0.00    0.00     0.00     0.00     0.00
+          39     39  cpuhp/4            0.19     0.00     0.00     0.00    0.00     0.00     0.00     0.00
+
+Dynamic interactive interface of delaytop::
+
+       # ./delaytop -p pid
+       Print delayacct stats
+
+       # ./delaytop -P num
+       Display the top N tasks
+
+       # ./delaytop -n num
+       Set delaytop refresh frequency (num times)
+
+       # ./delaytop -d secs
+       Specify refresh interval as secs