How do you find out why MacOS has a high load average?

Question

Recently, I noticed that MacOS (Catalina) is running slow. Apps regularly show the spinning rainbow wheel cursor, and video conference apps don't work. I had a load average of over 20, and after quitting all apps, I could only get it down to 16. Normally I see a load average of 1 to 3, even with all my apps open.

I resorted to rebooting my laptop, costing me hundreds of open windows in several apps. When the login screen appeared, I SSH'd into it from another machine. Without any graphical logins, the load average was already 13. I couldn't identify any apps that were consuming a lot of resources. There was some daemon that collects data for Spotlight to use, but it was only using 10% CPU according to top.

After logging in locally, the load average is back to 15 with just a couple of terminals running, and I'm already getting the rainbow cursor.

There's absolutely nothing suspicious in /var/log/system.log, nor in the output of dmesg.

MacOS has never worked very well, but it's never been this bad. How can I find out what it's doing and why?

EDIT: Here's the output of top with no local users:

Processes: 150 total, 2 running, 148 sleeping, 718 threads                                11:46:13
Load Avg: 11.63, 4.14, 1.62  CPU usage: 0.45% user, 62.52% sys, 37.1% idle
SharedLibs: 219M resident, 26M data, 24M linkedit.
MemRegions: 13721 total, 596M resident, 61M private, 349M shared.
PhysMem: 2847M used (1660M wired), 13G unused.
VM: 711G vsize, 1991M framework vsize, 0(0) swapins, 0(0) swapouts.
Networks: packets: 607/181K in, 917/272K out. Disks: 54410/873M read, 1852/14M written.

PID  COMMAND      %CPU TIME     #TH    #WQ  #POR MEM    PURG   CMPR PGRP PPID STATE    BOOSTS
287  mdsync       10.9 00:01.59 3      1    43   4524K+ 0B     0B   287  1    sleeping *0[1]
0    kernel_task  4.8  00:52.13 266/12 0    0    37M    0B     0B   0    0    running   0[0]
343  top          3.0  00:00.63 1/1    0    25   1868K  0B     0B   343  293  running  *0[1]
203  airportd     1.1  00:01.68 16     14   175+ 6248K+ 0B     0B   203  1    sleeping  0[10]
188  WindowServer 1.1  00:06.19 9      4    343  109M   1512K  0B   188  1    sleeping *0[1]
216  usbd         0.6  00:00.53 3      2    90+  2992K  0B     0B   216  1    sleeping  0[0]
59   configd      0.4  00:01.94 11     4    330+ 4144K  0B     0B   59   1    sleeping *0[1]
269  SecurityAgen 0.4  00:04.36 3      1    287  248M   2052K  0B   269  1    sleeping *0[1]
49   UserEventAge 0.2  00:01.71 6      3    410  4184K  0B     0B   49   1    sleeping *0[1]
1    launchd      0.1  00:03.21 3      2    1433 10M    0B     0B   1    0    sleeping  0[0]
58   systemstats  0.1  00:01.04 3      2    97   4132K+ 0B     0B   58   1    sleeping  0[1]
106  AirPlayXPCHe 0.1  00:00.62 6      3    167+ 4132K+ 0B     0B   106  1    sleeping *0[1]
143  contextstore 0.1  00:00.90 4      3    107+ 5232K+ 236K   0B   143  1    sleeping  0[52]
96   PerfPowerSer 0.1  00:02.70 8      5    275  9912K  256K   0B   96   1    sleeping  0[14]
218  VDCAssistant 0.0  00:00.17 2      1    28   2856K  0B     0B   218  1    sleeping *0[1]
61   powerd       0.0  00:00.82 3      2    100  2676K  0B     0B   61   1    sleeping *0[1]
107  notifyd      0.0  00:00.62 2      1    137  972K   0B     0B   107  1    sleeping *0[1]
102  bluetoothd   0.0  00:00.51 3      2    111+ 4132K  0B     0B   102  1    sleeping *0[1]
292  sshd         0.0  00:00.01 1      0    19   1036K  0B     0B   288  288  sleeping *0[1]
251  TouchBarServ 0.0  00:00.47 4      1    254  12M    5888K  0B   251  1    sleeping *0[1]
103  hidd         0.0  00:00.86 6      2    268  3076K  0B     0B   103  1    sleeping *0[1]

Answer 1

Usually this type of behavior is observed when there is a hardware problem. Often this is due to either a problem with the disk system (i.e. drive or controller) or lack of proper cooling (i.e. failed fan).

I would suggest ensuring that you have proper backups, then try to inspect the fans and clean them. Or alternatively send it in for repairs (or consider a new laptop if the current one is really old).