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This patch optimizes the generic spinlock code. The type pthread_spinlock_t is a typedef to volatile int on all archs. Passing a volatile pointer to the atomic macros which are not mapped to the C11 atomic builtins can lead to extra stores and loads to stack if such a macro creates a temporary variable by using "__typeof (*(mem)) tmp;". Thus, those macros which are used by spinlock code - atomic_exchange_acquire, atomic_load_relaxed, atomic_compare_exchange_weak - have to be adjusted. According to the comment from Szabolcs Nagy, the type of a cast expression is unqualified (see http://www.open-std.org/jtc1/sc22/wg14/www/docs/dr_423.htm): __typeof ((__typeof (*(mem)) *(mem)) tmp; Thus from spinlock perspective the variable tmp is of type int instead of type volatile int. This patch adjusts those macros in include/atomic.h. With this construct GCC >= 5 omits the extra stores and loads. The atomic macros are replaced by the C11 like atomic macros and thus the code is aligned to it. The pthread_spin_unlock implementation is now using release memory order instead of sequentially consistent memory order. The issue with passed volatile int pointers applies to the C11 like atomic macros as well as the ones used before. I've added a glibc_likely hint to the first atomic exchange in pthread_spin_lock in order to return immediately to the caller if the lock is free. Without the hint, there is an additional jump if the lock is free. I've added the atomic_spin_nop macro within the loop of plain reads. The plain reads are also realized by C11 like atomic_load_relaxed macro. The new define ATOMIC_EXCHANGE_USES_CAS determines if the first try to acquire the spinlock in pthread_spin_lock or pthread_spin_trylock is an exchange or a CAS. This is defined in atomic-machine.h for all architectures. The define SPIN_LOCK_READS_BETWEEN_CMPXCHG is now removed. There is no technical reason for throwing in a CAS every now and then, and so far we have no evidence that it can improve performance. If that would be the case, we have to adjust other spin-waiting loops elsewhere, too! Using a CAS loop without plain reads is not a good idea on many targets and wasn't used by one. Thus there is now no option to do so. Architectures are now using the generic spinlock automatically if they do not provide an own implementation. Thus the pthread_spin_lock.c files in sysdeps folder are deleted. ChangeLog: * NEWS: Mention new spinlock implementation. * include/atomic.h: (__atomic_val_bysize): Cast type to omit volatile qualifier. (atomic_exchange_acq): Likewise. (atomic_load_relaxed): Likewise. (ATOMIC_EXCHANGE_USES_CAS): Check definition. * nptl/pthread_spin_init.c (pthread_spin_init): Use atomic_store_relaxed. * nptl/pthread_spin_lock.c (pthread_spin_lock): Use C11-like atomic macros. * nptl/pthread_spin_trylock.c (pthread_spin_trylock): Likewise. * nptl/pthread_spin_unlock.c (pthread_spin_unlock): Use atomic_store_release. * sysdeps/aarch64/nptl/pthread_spin_lock.c: Delete File. * sysdeps/arm/nptl/pthread_spin_lock.c: Likewise. * sysdeps/hppa/nptl/pthread_spin_lock.c: Likewise. * sysdeps/m68k/nptl/pthread_spin_lock.c: Likewise. * sysdeps/microblaze/nptl/pthread_spin_lock.c: Likewise. * sysdeps/mips/nptl/pthread_spin_lock.c: Likewise. * sysdeps/nios2/nptl/pthread_spin_lock.c: Likewise. * sysdeps/aarch64/atomic-machine.h (ATOMIC_EXCHANGE_USES_CAS): Define. * sysdeps/alpha/atomic-machine.h: Likewise. * sysdeps/arm/atomic-machine.h: Likewise. * sysdeps/i386/atomic-machine.h: Likewise. * sysdeps/ia64/atomic-machine.h: Likewise. * sysdeps/m68k/coldfire/atomic-machine.h: Likewise. * sysdeps/m68k/m680x0/m68020/atomic-machine.h: Likewise. * sysdeps/microblaze/atomic-machine.h: Likewise. * sysdeps/mips/atomic-machine.h: Likewise. * sysdeps/powerpc/powerpc32/atomic-machine.h: Likewise. * sysdeps/powerpc/powerpc64/atomic-machine.h: Likewise. * sysdeps/s390/atomic-machine.h: Likewise. * sysdeps/sparc/sparc32/atomic-machine.h: Likewise. * sysdeps/sparc/sparc32/sparcv9/atomic-machine.h: Likewise. * sysdeps/sparc/sparc64/atomic-machine.h: Likewise. * sysdeps/tile/tilegx/atomic-machine.h: Likewise. * sysdeps/tile/tilepro/atomic-machine.h: Likewise. * sysdeps/unix/sysv/linux/hppa/atomic-machine.h: Likewise. * sysdeps/unix/sysv/linux/m68k/coldfire/atomic-machine.h: Likewise. * sysdeps/unix/sysv/linux/nios2/atomic-machine.h: Likewise. * sysdeps/unix/sysv/linux/sh/atomic-machine.h: Likewise. * sysdeps/x86_64/atomic-machine.h: Likewise.
95 lines
3.2 KiB
C
95 lines
3.2 KiB
C
/* Copyright (C) 2003-2017 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Carlos O'Donell <carlos@baldric.uwo.ca>, 2005.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library. If not, see
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<http://www.gnu.org/licenses/>. */
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#include <stdint.h> /* Required for type definitions e.g. uint8_t. */
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#ifndef _ATOMIC_MACHINE_H
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#define _ATOMIC_MACHINE_H 1
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typedef int8_t atomic8_t;
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typedef uint8_t uatomic8_t;
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typedef int_fast8_t atomic_fast8_t;
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typedef uint_fast8_t uatomic_fast8_t;
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typedef int32_t atomic32_t;
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typedef uint32_t uatomic32_t;
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typedef int_fast32_t atomic_fast32_t;
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typedef uint_fast32_t uatomic_fast32_t;
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typedef intptr_t atomicptr_t;
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typedef uintptr_t uatomicptr_t;
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typedef intmax_t atomic_max_t;
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typedef uintmax_t uatomic_max_t;
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#define __HAVE_64B_ATOMICS 0
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#define USE_ATOMIC_COMPILER_BUILTINS 0
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/* XXX Is this actually correct? */
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#define ATOMIC_EXCHANGE_USES_CAS 1
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/* prev = *addr;
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if (prev == old)
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*addr = new;
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return prev; */
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/* Use the kernel atomic light weight syscalls on hppa. */
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#define _LWS "0xb0"
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#define _LWS_CAS "0"
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/* Note r31 is the link register. */
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#define _LWS_CLOBBER "r1", "r23", "r22", "r20", "r31", "memory"
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/* String constant for -EAGAIN. */
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#define _ASM_EAGAIN "-11"
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/* String constant for -EDEADLOCK. */
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#define _ASM_EDEADLOCK "-45"
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/* The only basic operation needed is compare and exchange. The mem
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pointer must be word aligned. We no longer loop on deadlock. */
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#define atomic_compare_and_exchange_val_acq(mem, newval, oldval) \
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({ \
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register long lws_errno asm("r21"); \
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register unsigned long lws_ret asm("r28"); \
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register unsigned long lws_mem asm("r26") = (unsigned long)(mem); \
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register unsigned long lws_old asm("r25") = (unsigned long)(oldval);\
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register unsigned long lws_new asm("r24") = (unsigned long)(newval);\
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__asm__ __volatile__( \
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"0: \n\t" \
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"ble " _LWS "(%%sr2, %%r0) \n\t" \
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"ldi " _LWS_CAS ", %%r20 \n\t" \
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"cmpiclr,<> " _ASM_EAGAIN ", %%r21, %%r0\n\t" \
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"b,n 0b \n\t" \
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"cmpclr,= %%r0, %%r21, %%r0 \n\t" \
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"iitlbp %%r0,(%%sr0, %%r0) \n\t" \
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: "=r" (lws_ret), "=r" (lws_errno) \
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: "r" (lws_mem), "r" (lws_old), "r" (lws_new) \
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: _LWS_CLOBBER \
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); \
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\
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(__typeof (oldval)) lws_ret; \
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})
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#define atomic_compare_and_exchange_bool_acq(mem, newval, oldval) \
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({ \
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__typeof__ (*mem) ret; \
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ret = atomic_compare_and_exchange_val_acq(mem, newval, oldval); \
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/* Return 1 if it was already acquired. */ \
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(ret != oldval); \
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})
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#endif
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/* _ATOMIC_MACHINE_H */
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