Bug 184048 - developers handbook, 10.7 Debugging Deadlocks - must include warning on DIAGNOSTIC adding too much overhead
Summary: developers handbook, 10.7 Debugging Deadlocks - must include warning on DIAGN...
Status: Open
Alias: None
Product: Documentation
Classification: Unclassified
Component: Documentation (show other bugs)
Version: Latest
Hardware: Any Any
: Normal Affects Only Me
Assignee: freebsd-doc mailing list
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2013-11-18 09:40 UTC by Anton Shterenlikht
Modified: 2017-12-31 22:27 UTC (History)
0 users

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Description Anton Shterenlikht 2013-11-18 09:40:00 UTC
http://www.freebsd.org/doc/en/books/developers-handbook/kerneldebug-deadlocks.html

My experience with ia64 -current shows that
kernel option DIAGNOSTIC adds too much overhead
to the system. It seems the extra debugging
consumes 100% of system resources and the system
can do nothing else. In particular, the symptoms are:

- kernel thread taskq, which consumes 100% CPU, e.g.:

  PID USERNAME   PRI NICE   SIZE    RES STATE   C   TIME     CPU COMMAND
    0 root         8    0     0K   416K CPU0    0 186:02 100.00% kernel{thread taskq}

- system extremely unresponsive, requiring over 1 min(!)
  to execute ls, df, ps, date, uptime, etc.

- lots of messages similar to:

Expensive timeout(9) function: 0x9ffc000000dca8b0(0) 0.036993424 s

Fix: 

Removing DIAGNOSTIC gets the system back to usable.

I suggest adding a warning to the above page, something
like: "Be warned that option DIAGNOSTIC adds a lot of
extra overheads to the system, which can result in very
noticeable degradation of performance."
And then listing the above sysmptoms as examples of
degraded performance.
Or something like this.

I've discussed this with marcel@ and he agrees with me.
Comment 1 Mark Linimon freebsd_committer freebsd_triage 2013-11-19 01:47:12 UTC
Responsible Changed
From-To: freebsd-bugs->freebsd-doc

reclassify.
Comment 2 Eitan Adler freebsd_committer freebsd_triage 2017-12-31 07:59:31 UTC
For bugs matching the following criteria:

Status: In Progress Changed: (is less than) 2014-06-01

Reset to default assignee and clear in-progress tags.

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