cvs commit: src/sys/conf files src/sys/kern kern_mutex.c kern_thread.c subr_turnstile.c subr_witness.c src/sys/sys _mutex.h filedesc.h proc.h

[John Baldwin]

jhb         2003/11/11 14:07:30 PST

  FreeBSD src repository

  Modified files:
    sys/conf             files 
    sys/kern             kern_mutex.c kern_thread.c 
                         subr_turnstile.c subr_witness.c 
    sys/sys              _mutex.h filedesc.h proc.h 
  Log:
  Add an implementation of turnstiles and change the sleep mutex code to use
  turnstiles to implement blocking isntead of implementing a thread queue
  directly.  These turnstiles are somewhat similar to those used in Solaris 7
  as described in Solaris Internals but are also different.
  
  Turnstiles do not come out of a fixed-sized pool.  Rather, each thread is
  assigned a turnstile when it is created that it frees when it is destroyed.
  When a thread blocks on a lock, it donates its turnstile to that lock to
  serve as queue of blocked threads.  The queue associated with a given lock
  is found by a lookup in a simple hash table.  The turnstile itself is
  protected by a lock associated with its entry in the hash table.  This
  means that sched_lock is no longer needed to contest on a mutex.  Instead,
  sched_lock is only used when manipulating run queues or thread priorities.
  Turnstiles also implement priority propagation inherently.
  
  Currently turnstiles only support mutexes.  Eventually, however, turnstiles
  may grow two queue's to support a non-sleepable reader/writer lock
  implementation.  For more details, see the comments in sys/turnstile.h and
  kern/subr_turnstile.c.
  
  The two primary advantages from the turnstile code include: 1) the size
  of struct mutex shrinks by four pointers as it no longer stores the
  thread queue linkages directly, and 2) less contention on sched_lock in
  SMP systems including the ability for multiple CPUs to contend on different
  locks simultaneously (not that this last detail is necessarily that much of
  a big win).  Note that 1) means that this commit is a kernel ABI breaker,
  so don't mix old modules with a new kernel and vice versa.
  
  Tested on:      i386 SMP, sparc64 SMP, alpha SMP
  
  Revision  Changes    Path
  1.848     +1 -0      src/sys/conf/files
  1.132     +39 -225   src/sys/kern/kern_mutex.c
  1.162     +3 -0      src/sys/kern/kern_thread.c
  1.132     +471 -758  src/sys/kern/subr_turnstile.c
  1.162     +3 -3      src/sys/kern/subr_witness.c
  1.10      +0 -2      src/sys/sys/_mutex.h
  1.52      +2 -0      src/sys/sys/filedesc.h
  1.357     +8 -4      src/sys/sys/proc.h