cvs commit: src/sys/kern init_main.c kern_exit.c kern_fork.c kern_ktrace.c kern_proc.c subr_trap.c src/sys/sys ktrace.h proc.h

Robert Watson rwatson at
Sun Nov 13 13:27:45 GMT 2005

rwatson     2005-11-13 13:27:44 UTC

  FreeBSD src repository

  Modified files:
    sys/kern             init_main.c kern_exit.c kern_fork.c 
                         kern_ktrace.c kern_proc.c subr_trap.c 
    sys/sys              ktrace.h proc.h 
  Moderate rewrite of kernel ktrace code to attempt to generally improve
  reliability when tracing fast-moving processes or writing traces to
  slow file systems by avoiding unbounded queueuing and dropped records.
  Record loss was previously possible when the global pool of records
  become depleted as a result of record generation outstripping record
  commit, which occurred quickly in many common situations.
  These changes partially restore the 4.x model of committing ktrace
  records at the point of trace generation (synchronous), but maintain
  the 5.x deferred record commit behavior (asynchronous) for situations
  where entering VFS and sleeping is not possible (i.e., in the
  scheduler).  Records are now queued per-process as opposed to
  globally, with processes responsible for committing records from their
  own context as required.
  - Eliminate the ktrace worker thread and global record queue, as they
    are no longer used.  Keep the global free record list, as records
    are still used.
  - Add a per-process record queue, which will hold any asynchronously
    generated records, such as from context switches.  This replaces the
    global queue as the place to submit asynchronous records to.
  - When a record is committed asynchronously, simply queue it to the
  - When a record is committed synchronously, first drain any pending
    per-process records in order to maintain ordering as best we can.
    Currently ordering between competing threads is provided via a global
    ktrace_sx, but a per-process flag or lock may be desirable in the
  - When a process returns to user space following a system call, trap,
    signal delivery, etc, flush any pending records.
  - When a process exits, flush any pending records.
  - Assert on process tear-down that there are no pending records.
  - Slightly abstract the notion of being "in ktrace", which is used to
    prevent the recursive generation of records, as well as generating
    traces for ktrace events.
  Future work here might look at changing the set of events marked for
  synchronous and asynchronous record generation, re-balancing queue
  depth, timeliness of commit to disk, and so on.  I.e., performing a
  drain every (n) records.
  MFC after:      1 month
  Discussed with: jhb
  Requested by:   Marc Olzheim <marcolz at stack dot nl>
  Revision  Changes    Path
  1.259     +1 -0      src/sys/kern/init_main.c
  1.273     +3 -1      src/sys/kern/kern_exit.c
  1.253     +1 -0      src/sys/kern/kern_fork.c
  1.104     +191 -91   src/sys/kern/kern_ktrace.c
  1.235     +1 -0      src/sys/kern/kern_proc.c
  1.283     +4 -0      src/sys/kern/subr_trap.c
  1.32      +11 -0     src/sys/sys/ktrace.h
  1.443     +1 -0      src/sys/sys/proc.h

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