linux/arch/x86/lib/rwlock.S
Jan Beulich a750036f35 x86: Fix write lock scalability 64-bit issue
With the write lock path simply subtracting RW_LOCK_BIAS there
is, on large systems, the theoretical possibility of overflowing
the 32-bit value that was used so far (namely if 128 or more
CPUs manage to do the subtraction, but don't get to do the
inverse addition in the failure path quickly enough).

A first measure is to modify RW_LOCK_BIAS itself - with the new
value chosen, it is good for up to 2048 CPUs each allowed to
nest over 2048 times on the read path without causing an issue.
Quite possibly it would even be sufficient to adjust the bias a
little further, assuming that allowing for significantly less
nesting would suffice.

However, as the original value chosen allowed for even more
nesting levels, to support more than 2048 CPUs (possible
currently only for 64-bit kernels) the lock itself gets widened
to 64 bits.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/4E258E0D020000780004E3F0@nat28.tlf.novell.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-07-21 09:03:36 +02:00

45 lines
783 B
ArmAsm

/* Slow paths of read/write spinlocks. */
#include <linux/linkage.h>
#include <asm/alternative-asm.h>
#include <asm/frame.h>
#include <asm/rwlock.h>
#ifdef CONFIG_X86_32
# define __lock_ptr eax
#else
# define __lock_ptr rdi
#endif
ENTRY(__write_lock_failed)
CFI_STARTPROC
FRAME
0: LOCK_PREFIX
WRITE_LOCK_ADD($RW_LOCK_BIAS) (%__lock_ptr)
1: rep; nop
cmpl $WRITE_LOCK_CMP, (%__lock_ptr)
jne 1b
LOCK_PREFIX
WRITE_LOCK_SUB($RW_LOCK_BIAS) (%__lock_ptr)
jnz 0b
ENDFRAME
ret
CFI_ENDPROC
END(__write_lock_failed)
ENTRY(__read_lock_failed)
CFI_STARTPROC
FRAME
0: LOCK_PREFIX
READ_LOCK_SIZE(inc) (%__lock_ptr)
1: rep; nop
READ_LOCK_SIZE(cmp) $1, (%__lock_ptr)
js 1b
LOCK_PREFIX
READ_LOCK_SIZE(dec) (%__lock_ptr)
js 0b
ENDFRAME
ret
CFI_ENDPROC
END(__read_lock_failed)