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locking/rwsem: Remove arch specific rwsem files

Telusuri Sumber 
As the generic rwsem-xadd code is using the appropriate acquire and
release versions of the atomic operations, the arch specific rwsem.h
files will not be that much faster than the generic code as long as the
atomic functions are properly implemented. So we can remove those arch
specific rwsem.h and stop building asm/rwsem.h to reduce maintenance
effort.

Currently, only x86, alpha and ia64 have implemented architecture
specific fast paths. I don't have access to alpha and ia64 systems for
testing, but they are legacy systems that are not likely to be updated
to the latest kernel anyway.

By using a rwsem microbenchmark, the total locking rates on a 4-socket
56-core 112-thread x86-64 system before and after the patch were as
follows (mixed means equal # of read and write locks):

                      Before Patch              After Patch
   # of Threads  wlock   rlock   mixed     wlock   rlock   mixed
   ------------  -----   -----   -----     -----   -----   -----
        1        29,201  30,143  29,458    28,615  30,172  29,201
        2         6,807  13,299   1,171     7,725  15,025   1,804
        4         6,504  12,755   1,520     7,127  14,286   1,345
        8         6,762  13,412     764     6,826  13,652     726
       16         6,693  15,408     662     6,599  15,938     626
       32         6,145  15,286     496     5,549  15,487     511
       64         5,812  15,495      60     5,858  15,572      60

There were some run-to-run variations for the multi-thread tests. For
x86-64, using the generic C code fast path seems to be a little bit
faster than the assembly version with low lock contention.  Looking at
the assembly version of the fast paths, there are assembly to/from C
code wrappers that save and restore all the callee-clobbered registers
(7 registers on x86-64). The assembly generated from the generic C
code doesn't need to do that. That may explain the slight performance
gain here.

The generic asm rwsem.h can also be merged into kernel/locking/rwsem.h
with no code change as no other code other than those under
kernel/locking needs to access the internal rwsem macros and functions.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-c6x-dev@linux-c6x.org
Cc: linux-m68k@lists.linux-m68k.org
Cc: linux-riscv@lists.infradead.org
Cc: linux-um@lists.infradead.org
Cc: linux-xtensa@linux-xtensa.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: nios2-dev@lists.rocketboards.org
Cc: openrisc@lists.librecores.org
Cc: uclinux-h8-devel@lists.sourceforge.jp
Link: https://lkml.kernel.org/r/20190322143008.21313-2-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Waiman Long
2019-03-22 10:30:06 -04:00
committed by Ingo Molnar
orang tua a1247d06d0
melakukan 46ad0840b1
19 mengubah file dengan 134 tambahan dan 932 penghapusan
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172
arch/ia64/include/asm/rwsem.h
Melihat File

@@ -1,172 +0,0 @@
/* SPDX-License-Identifier: GPL-2.0 */
/*
* R/W semaphores for ia64
*
* Copyright (C) 2003 Ken Chen <kenneth.w.chen@intel.com>
* Copyright (C) 2003 Asit Mallick <asit.k.mallick@intel.com>
* Copyright (C) 2005 Christoph Lameter <cl@linux.com>
*
* Based on asm-i386/rwsem.h and other architecture implementation.
*
* The MSW of the count is the negated number of active writers and
* waiting lockers, and the LSW is the total number of active locks.
*
* The lock count is initialized to 0 (no active and no waiting lockers).
*
* When a writer subtracts WRITE_BIAS, it'll get 0xffffffff00000001 for
* the case of an uncontended lock. Readers increment by 1 and see a positive
* value when uncontended, negative if there are writers (and maybe) readers
* waiting (in which case it goes to sleep).
*/
#ifndef _ASM_IA64_RWSEM_H
#define _ASM_IA64_RWSEM_H
#ifndef _LINUX_RWSEM_H
#error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead."
#endif
#include <asm/intrinsics.h>
#define RWSEM_UNLOCKED_VALUE __IA64_UL_CONST(0x0000000000000000)
#define RWSEM_ACTIVE_BIAS (1L)
#define RWSEM_ACTIVE_MASK (0xffffffffL)
#define RWSEM_WAITING_BIAS (-0x100000000L)
#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
/*
* lock for reading
*/
static inline int
___down_read (struct rw_semaphore *sem)
{
long result = ia64_fetchadd8_acq((unsigned long *)&sem->count.counter, 1);
return (result < 0);
}
static inline void
__down_read (struct rw_semaphore *sem)
{
if (___down_read(sem))
rwsem_down_read_failed(sem);
}
static inline int
__down_read_killable (struct rw_semaphore *sem)
{
if (___down_read(sem))
if (IS_ERR(rwsem_down_read_failed_killable(sem)))
return -EINTR;
return 0;
}
/*
* lock for writing
*/
static inline long
___down_write (struct rw_semaphore *sem)
{
long old, new;
do {
old = atomic_long_read(&sem->count);
new = old + RWSEM_ACTIVE_WRITE_BIAS;
} while (atomic_long_cmpxchg_acquire(&sem->count, old, new) != old);
return old;
}
static inline void
__down_write (struct rw_semaphore *sem)
{
if (___down_write(sem))
rwsem_down_write_failed(sem);
}
static inline int
__down_write_killable (struct rw_semaphore *sem)
{
if (___down_write(sem)) {
if (IS_ERR(rwsem_down_write_failed_killable(sem)))
return -EINTR;
}
return 0;
}
/*
* unlock after reading
*/
static inline void
__up_read (struct rw_semaphore *sem)
{
long result = ia64_fetchadd8_rel((unsigned long *)&sem->count.counter, -1);
if (result < 0 && (--result & RWSEM_ACTIVE_MASK) == 0)
rwsem_wake(sem);
}
/*
* unlock after writing
*/
static inline void
__up_write (struct rw_semaphore *sem)
{
long old, new;
do {
old = atomic_long_read(&sem->count);
new = old - RWSEM_ACTIVE_WRITE_BIAS;
} while (atomic_long_cmpxchg_release(&sem->count, old, new) != old);
if (new < 0 && (new & RWSEM_ACTIVE_MASK) == 0)
rwsem_wake(sem);
}
/*
* trylock for reading -- returns 1 if successful, 0 if contention
*/
static inline int
__down_read_trylock (struct rw_semaphore *sem)
{
long tmp;
while ((tmp = atomic_long_read(&sem->count)) >= 0) {
if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp, tmp+1)) {
return 1;
}
}
return 0;
}
/*
* trylock for writing -- returns 1 if successful, 0 if contention
*/
static inline int
__down_write_trylock (struct rw_semaphore *sem)
{
long tmp = atomic_long_cmpxchg_acquire(&sem->count,
RWSEM_UNLOCKED_VALUE, RWSEM_ACTIVE_WRITE_BIAS);
return tmp == RWSEM_UNLOCKED_VALUE;
}
/*
* downgrade write lock to read lock
*/
static inline void
__downgrade_write (struct rw_semaphore *sem)
{
long old, new;
do {
old = atomic_long_read(&sem->count);
new = old - RWSEM_WAITING_BIAS;
} while (atomic_long_cmpxchg_release(&sem->count, old, new) != old);
if (old < 0)
rwsem_downgrade_wake(sem);
}
#endif /* _ASM_IA64_RWSEM_H */