[PATCH 2/2] New pthread rwlock that is more scalable.

[Torvald Riegel]

This replaces the pthread rwlock with a new implementation that uses a
more scalable algorithm (primarily through not using a critical section
anymore to make state changes).  The fast path for rdlock acquisition
and release is now basically a single atomic read-modify write or CAS
and a few branches.  See nptl/pthread_rwlock_common.c for details.

Tested on x86_64-linux.

        * nptl/DESIGN-rwlock.txt: Remove.
        * nptl/lowlevelrwlock.sym: Remove.
        * nptl/Makefile: Add new tests.
        * nptl/pthread_rwlock_common.c: New file.  Contains the new rwlock.
        * nptl/pthreadP.h (PTHREAD_RWLOCK_PREFER_READER_P): Remove.
        (PTHREAD_RWLOCK_WRPHASE, PTHREAD_RWLOCK_WRLOCKED,
        PTHREAD_RWLOCK_RWAITING, PTHREAD_RWLOCK_READER_SHIFT,
        PTHREAD_RWLOCK_READER_OVERFLOW, PTHREAD_RWLOCK_WRHANDOVER,
        PTHREAD_RWLOCK_FUTEX_USED): New.
        * nptl/pthread_rwlock_init.c (__pthread_rwlock_init): Adapt to new
        implementation.
        * nptl/pthread_rwlock_rdlock.c (__pthread_rwlock_rdlock_slow): Remove.
        (__pthread_rwlock_rdlock): Adapt.
        * nptl/pthread_rwlock_timedrdlock.c
        (pthread_rwlock_timedrdlock): Adapt.
        * nptl/pthread_rwlock_timedwrlock.c
        (pthread_rwlock_timedwrlock): Adapt.
        * nptl/pthread_rwlock_trywrlock.c (pthread_rwlock_trywrlock): Adapt.
        * nptl/pthread_rwlock_tryrdlock.c (pthread_rwlock_tryrdlock): Adapt.
        * nptl/pthread_rwlock_unlock.c (pthread_rwlock_unlock): Adapt.
        * nptl/pthread_rwlock_wrlock.c (__pthread_rwlock_wrlock_slow): Remove.
        (__pthread_rwlock_wrlock): Adapt.
        * nptl/tst-rwlock10.c: Adapt.
        * nptl/tst-rwlock11.c: Adapt.
        * nptl/tst-rwlock17.c: New file.
        * nptl/tst-rwlock18.c: New file.
        * nptl/tst-rwlock19.c: New file.
        * nptl/tst-rwlock2b.c: New file.
        * nptl/tst-rwlock8.c: Adapt.
        * nptl/tst-rwlock9.c: Adapt.
        * sysdeps/aarch64/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
        * sysdeps/arm/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
        * sysdeps/hppa/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
        * sysdeps/ia64/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
        * sysdeps/m68k/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
        * sysdeps/microblaze/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
        * sysdeps/mips/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
        * sysdeps/nios2/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
        * sysdeps/s390/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
        * sysdeps/sh/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
        * sysdeps/sparc/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
        * sysdeps/tile/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
        * sysdeps/unix/sysv/linux/alpha/bits/pthreadtypes.h
        (pthread_rwlock_t): Adapt.
        * sysdeps/unix/sysv/linux/powerpc/bits/pthreadtypes.h
        (pthread_rwlock_t): Adapt.
        * sysdeps/x86/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.

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