cvs commit: src/lib/libthr/thread thr_mutex.c src/lib/libkse/thread thr_mutex.c src/include pthread.h

[Kris Kennaway]

kris        2007-10-29 21:01:47 UTC

  FreeBSD src repository

  Modified files:
    lib/libthr/thread    thr_mutex.c 
    lib/libkse/thread    thr_mutex.c 
    include              pthread.h 
  Log:
  Add a new "non-portable" mutex type, PTHREAD_MUTEX_ADAPTIVE_NP.  This
  is also implemented in glibc and is used by a number of existing
  applications (mysql, firefox, etc).
  
  This mutex type is a default mutex with the additional property that
  it spins briefly when attempting to acquire a contested lock, doing
  trylock operations in userland before entering the kernel to block if
  eventually unsuccessful.
  
  The expectation is that applications requesting this mutex type know
  that the mutex is likely to be only held for very brief periods, so it
  is faster to spin in userland and probably succeed in acquiring the
  mutex, than to enter the kernel and sleep, only to be woken up almost
  immediately.  This can help significantly in certain cases when
  pthread mutexes are heavily contended and held for brief durations
  (such as mysql).
  
  Spin up to 200 times before entering the kernel, which represents only
  a few us on modern CPUs.  No performance degradation was observed with
  this value and it is sufficient to avoid a large performance drop in
  mysql performance in the heavily contended pthread mutex case.
  
  The libkse implementation is a NOP.
  
  Reviewed by:      jeff
  MFC after:        3 days
  
  Revision  Changes    Path
  1.41      +2 -0      src/include/pthread.h
  1.54      +3 -0      src/lib/libkse/thread/thr_mutex.c
  1.55      +29 -0     src/lib/libthr/thread/thr_mutex.c