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    Subject[087/139] x86-64: support native xadd rwsem implementation
    2.6.33-stable review patch.  If anyone has any objections, please let us know.

    ------------------

    From: Linus Torvalds <torvalds@linux-foundation.org>

    commit bafaecd11df15ad5b1e598adc7736afcd38ee13d upstream.

    This one is much faster than the spinlock based fallback rwsem code,
    with certain artifical benchmarks having shown 300%+ improvement on
    threaded page faults etc.

    Again, note the 32767-thread limit here. So this really does need that
    whole "make rwsem_count_t be 64-bit and fix the BIAS values to match"
    extension on top of it, but that is conceptually a totally independent
    issue.

    NOT TESTED! The original patch that this all was based on were tested by
    KAMEZAWA Hiroyuki, but maybe I screwed up something when I created the
    cleaned-up series, so caveat emptor..

    Also note that it _may_ be a good idea to mark some more registers
    clobbered on x86-64 in the inline asms instead of saving/restoring them.
    They are inline functions, but they are only used in places where there
    are not a lot of live registers _anyway_, so doing for example the
    clobbers of %r8-%r11 in the asm wouldn't make the fast-path code any
    worse, and would make the slow-path code smaller.

    (Not that the slow-path really matters to that degree. Saving a few
    unnecessary registers is the _least_ of our problems when we hit the slow
    path. The instruction/cycle counting really only matters in the fast
    path).

    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    LKML-Reference: <alpine.LFD.2.00.1001121810410.17145@localhost.localdomain>
    Signed-off-by: H. Peter Anvin <hpa@zytor.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    arch/x86/Kconfig.cpu | 2 -
    arch/x86/lib/Makefile | 1
    arch/x86/lib/rwsem_64.S | 81 ++++++++++++++++++++++++++++++++++++++++++++++++
    3 files changed, 83 insertions(+), 1 deletion(-)

    --- a/arch/x86/Kconfig.cpu
    +++ b/arch/x86/Kconfig.cpu
    @@ -319,7 +319,7 @@ config X86_L1_CACHE_SHIFT

    config X86_XADD
    def_bool y
    - depends on X86_32 && !M386
    + depends on X86_64 || !M386

    config X86_PPRO_FENCE
    bool "PentiumPro memory ordering errata workaround"
    --- a/arch/x86/lib/Makefile
    +++ b/arch/x86/lib/Makefile
    @@ -39,4 +39,5 @@ else
    lib-y += thunk_64.o clear_page_64.o copy_page_64.o
    lib-y += memmove_64.o memset_64.o
    lib-y += copy_user_64.o rwlock_64.o copy_user_nocache_64.o
    + lib-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem_64.o
    endif
    --- /dev/null
    +++ b/arch/x86/lib/rwsem_64.S
    @@ -0,0 +1,81 @@
    +/*
    + * x86-64 rwsem wrappers
    + *
    + * This interfaces the inline asm code to the slow-path
    + * C routines. We need to save the call-clobbered regs
    + * that the asm does not mark as clobbered, and move the
    + * argument from %rax to %rdi.
    + *
    + * NOTE! We don't need to save %rax, because the functions
    + * will always return the semaphore pointer in %rax (which
    + * is also the input argument to these helpers)
    + *
    + * The following can clobber %rdx because the asm clobbers it:
    + * call_rwsem_down_write_failed
    + * call_rwsem_wake
    + * but %rdi, %rsi, %rcx, %r8-r11 always need saving.
    + */
    +
    +#include <linux/linkage.h>
    +#include <asm/rwlock.h>
    +#include <asm/alternative-asm.h>
    +#include <asm/frame.h>
    +#include <asm/dwarf2.h>
    +
    +#define save_common_regs \
    + pushq %rdi; \
    + pushq %rsi; \
    + pushq %rcx; \
    + pushq %r8; \
    + pushq %r9; \
    + pushq %r10; \
    + pushq %r11
    +
    +#define restore_common_regs \
    + popq %r11; \
    + popq %r10; \
    + popq %r9; \
    + popq %r8; \
    + popq %rcx; \
    + popq %rsi; \
    + popq %rdi
    +
    +/* Fix up special calling conventions */
    +ENTRY(call_rwsem_down_read_failed)
    + save_common_regs
    + pushq %rdx
    + movq %rax,%rdi
    + call rwsem_down_read_failed
    + popq %rdx
    + restore_common_regs
    + ret
    + ENDPROC(call_rwsem_down_read_failed)
    +
    +ENTRY(call_rwsem_down_write_failed)
    + save_common_regs
    + movq %rax,%rdi
    + call rwsem_down_write_failed
    + restore_common_regs
    + ret
    + ENDPROC(call_rwsem_down_write_failed)
    +
    +ENTRY(call_rwsem_wake)
    + decw %dx /* do nothing if still outstanding active readers */
    + jnz 1f
    + save_common_regs
    + movq %rax,%rdi
    + call rwsem_wake
    + restore_common_regs
    +1: ret
    + ENDPROC(call_rwsem_wake)
    +
    +/* Fix up special calling conventions */
    +ENTRY(call_rwsem_downgrade_wake)
    + save_common_regs
    + pushq %rdx
    + movq %rax,%rdi
    + call rwsem_downgrade_wake
    + popq %rdx
    + restore_common_regs
    + ret
    + ENDPROC(call_rwsem_downgrade_wake)



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