rwsem: let RWSEM_WAITING_BIAS represent any number of waiting threads
commitfd41b33435ada87323cc86b50959fbffe35192c8
authorMichel Lespinasse <walken@google.com>
Tue, 10 Aug 2010 00:21:18 +0000 (9 17:21 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Tue, 10 Aug 2010 03:45:11 +0000 (9 20:45 -0700)
tree6d2a7e79557e5de21bc91fce5b939c1f7dc1355c
parent70bdc6e0644f3535e93bac5c364ca199397e507e
rwsem: let RWSEM_WAITING_BIAS represent any number of waiting threads

Previously each waiting thread added a bias of RWSEM_WAITING_BIAS.  With
this change, the bias is added only once to indicate that the wait list is
non-empty.

This has a few nice properties which will be used in following changes:
- when the spinlock is held and the waiter list is known to be non-empty,
  count < RWSEM_WAITING_BIAS  <=>  there is an active writer on that sem
- count == RWSEM_WAITING_BIAS  <=>  there are waiting threads and no
                                     active readers/writers on that sem

Signed-off-by: Michel Lespinasse <walken@google.com>
Acked-by: David Howells <dhowells@redhat.com>
Cc: Mike Waychison <mikew@google.com>
Cc: Suleiman Souhlal <suleiman@google.com>
Cc: Ying Han <yinghan@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
lib/rwsem.c