KnownBugs [FreeBSD WIKI]

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====== Pmctools: Known Bugs ======

The current bug list may be viewed at the following [[http://code.google.com/p/pmctools/issues/list|issue tracker]].

===== Old bug list =====

This page lists known bugs in the PMC code.

  * Profiling of multi-threaded programs has bugs. The symptoms are that multi-threaded programs do not exit cleanly. (Reported by David Fresse).
  * pmcstat -P appears to be missing samples (reported by Niklas Sorensson).
  * PCSAMPLE event logs should indicate a CPU# that the sample was taken on. We could reuse the ''%%pl_usermode%%'' 'int' field for this, keeping the CPU# in a higher numbered bitfield.
  * On the AMD64, an INVARIANTS-enabled kernel reports a memory leak at module unload time for memory type "pmc".  It appears that a log buffer is being leaked (from the size of the leak).
  * Forcibly unloading the hwpmc(4) module when it is in use shows up other leaks.  (Reported by ''%%wkoszek@%%'').
  * A WITNESS/INVARIANTS enabled AMD64 kernel reports the following lock-order reversal:

<code>
hwpmc: TSC/1/0x20 K8/4/0x1ff
lock order reversal:
1st 0xffffffff80564ea0 pmc shared lock (pmc shared lock) @ /home/fcpi/src/sys/modules/hwpmc/../../dev/hwpmc/hwpmc_mod.c:2527
2nd 0xffffffff80564fc0 proctree (proctree) @ /home/fcpi/src/sys/kern/kern_fork.c:301
KDB: stack backtrace:
witness_checkorder() at witness_checkorder+0x4f9
_sx_slock() at _sx_slock+0x4d
fork1() at fork1+0xf5
kthread_create() at kthread_create+0x96
pmclog_configure_log() at pmclog_configure_log+0x12f
pmc_syscall_handler() at pmc_syscall_handler+0x1e6
syscall() at syscall+0x215
Xfast_syscall() at Xfast_syscall+0xa8
--- syscall (0, FreeBSD ELF64, nosys), rip = 0x8008dfa9c, rsp = 0x7fffffffe4e8, rbp = 0x7fffffffe510 ---
</code>

  * Only dump kernel and process mappings once per owner process and only when a sampling PMC is configured. Currently we always log mappings, but this information is useless for log files that are being used in counting mode.
  * (reported by v.sriram) pmc_start(3) sometimes does not cause the hardware counter to be started. Inserting a sleep(3) call after the pmc_start() call makes stuff work.  I thought I had fixed this bug!
  * (reported by ssouhlal@) running pmcstat -S on a dual AMD64 results in an occasional double fault. This is mitigated by using a separate stack for NMI interrupts.  Bumping up the KSTACK size does not help.
  * (reported by rwatson) pmcstat -S on a P4 HTT box caused a stray NMI if interrupted with a ^C. See -current for analysis: the NMI is probably being handled after the WRMSR in p4_stop_pmc turns off the PMC. [[http://code.google.com/p/pmctools/issues/detail?id=30&colspec=ID%20Type%20Status%20Priority%20Opsys%20Component%20Summary|Issue 30]]
  * (reported by alfred) hwpmc does not deal with sparse CPU numbering correctly.