[LU-17853] Negative value reported in req_waittime mdt

• Type: Bug
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.16.0
• Affects Version/s: Lustre 2.14.0
• Labels: easy
• Severity: 3
• Assignee: Fred Dilger
• Reporter: Nathaniel Clark

Description

ldlm.services.ldlm_canceld.stats=
snapshot_time             1714662722.986857642 secs.nsecs
req_waittime              101358239600 samples [usecs] -36 1855805 5530720965329 21563670935443407
req_qdepth                101358239600 samples [reqs] 0 1164 1893537183 7828947261
req_active                101358239600 samples [reqs] 1 23 152657095033 281200017837
req_timeout               101358239600 samples [secs] 1 218 6892805470378 468801155450006
reqbuf_avail              210996467581 samples [bufs] 0 155 13398749465845 850967459690601
ldlm_cancel               101358239600 samples [usecs] 1 211241571 1436530054018 108103493490971286

This doesn't appear to be a math error like LU-9683, but possibly caused by NTP.

ptlrpc uses ktime_get_real() for timing events where other modules use ktime_get() for timing.

ktime_get_real() "can jump backwards due to a leap second update, NTP adjustment settimeofday() operation from user space."

Issue Links

• is related to: LU-9683 Negative value reported for req_waittime mdt stat