cleanup-reboot is a feature that allows 'evil' tests (that kill processes, cause OOM, GPU hang recovery, longevity, stress) to clean up after themselves by rebooting. This cleanup allows following tests to not get impacted by having such tests scheduled before them.

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Details:
I picked a DUT that ran a bunch of tests in succession. This
http://cros-full-0004.mtv.corp.google.com/afe/#tab_id=view_job&object_id=189501981 
graphics_dEQP.gles3-master.hasty.6

It has a system log associated with it ('messages')
https://pantheon.corp.google.com/storage/browser/chromeos-autotest-results/189501981-chromeos-test/chromeos4-row4-rack6-host18/sysinfo

A bunch of graphics tests would like to have a reboot after them
src/third_party/autotest/files/client/site_tests$ grep reboot graphics_*/control*
graphics_GLBench/control:DEPENDENCIES='cleanup-reboot'
graphics_GLMark2/control:DEPENDENCIES='cleanup-reboot'
graphics_GLMark2/control.bvt:DEPENDENCIES='cleanup-reboot'
graphics_GpuReset/control:DEPENDENCIES='cleanup-reboot'
graphics_SanAngeles/control:DEPENDENCIES='cleanup-reboot'
graphics_SanAngeles/control.bvt:DEPENDENCIES='cleanup-reboot'

But the log shows no reboots in the timeframe
grep --binary-files=text -E "Booting Linux|autotest runtest" 189501981-chromeos-test%2Fchromeos4-row4-rack6-host18%2Fsysinfo%2Fmessages.txt 
2018-04-04T21:40:41.332978+00:00 INFO kernel: [    0.000000] Booting Linux on physical CPU 0x500
2018-04-04T14:44:59.430419-07:00 INFO kernel: [    0.000000] Booting Linux on physical CPU 0x500
2018-04-04T14:45:36.367457-07:00 INFO kernel: [    0.000000] Booting Linux on physical CPU 0x500
2018-04-04T14:46:03.250931-07:00 INFO kernel: [    0.000000] Booting Linux on physical CPU 0x500
2018-04-04T14:46:40.390631-07:00 INFO kernel: [    0.000000] Booting Linux on physical CPU 0x500
2018-04-04T19:37:26.634778-07:00 NOTICE root[3740]: autotest runtest graphics_Stress
2018-04-04T19:49:13.237306-07:00 NOTICE root[7558]: autotest runtest graphics_dEQP
2018-04-04T19:53:16.440668-07:00 NOTICE root[12094]: autotest runtest graphics_GLMark2
2018-04-04T19:56:10.613848-07:00 NOTICE root[13782]: autotest runtest graphics_dEQP
2018-04-04T20:12:25.703670-07:00 NOTICE root[16566]: autotest runtest graphics_dEQP
2018-04-04T20:23:58.797873-07:00 NOTICE root[19190]: autotest runtest graphics_Gbm
2018-04-04T20:25:47.534707-07:00 NOTICE root[20259]: autotest runtest graphics_VTSwitch
2018-04-04T20:29:08.158487-07:00 NOTICE root[22850]: autotest runtest graphics_SanAngeles

(Also closer inspection doesn't show any signs of reboot after graphics_GLMark2 or graphics_SanAngeles, timestamps and pids are monotonically increasing.)

The test list from the log above matches times/order from cautotest/ for host chromeos4-row4-rack6-host18 (and is attached).

 

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