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    Subject[PATCH][2.6-mm] Allow i386 to reenable interrupts on lock contention
    Hello Keith, Andrew,

    Following up on Keith's code, i adapted the i386 code to allow enabling
    interrupts during contested locks depending on previous interrupt
    enable status. Obviously there will be a text increase (only for non
    CONFIG_SPINLINE case), although it doesn't seem so bad, there will be an
    increased exit latency when we attempt a lock acquisition after spinning
    due to the extra instructions. How much this will affect performance i'm
    not sure yet as i haven't had time to micro bench.

    text data bss dec hex filename
    2628024 921731 0 3549755 362a3b vmlinux-after
    2621369 921731 0 3543100 36103c vmlinux-before
    2618313 919222 0 3537535 35fa7f vmlinux-spinline

    The code has been stress tested on a 16x NUMAQ (courtesy OSDL).

    Andrew, does this email have a whitespace problem too?

    Index: linux-2.6.6-rc3-mm1/include/asm-i386/spinlock.h
    ===================================================================
    RCS file: /home/cvsroot/linux-2.6.6-rc3-mm1/include/asm-i386/spinlock.h,v
    retrieving revision 1.1.1.1
    diff -u -p -B -r1.1.1.1 spinlock.h
    --- linux-2.6.6-rc3-mm1/include/asm-i386/spinlock.h 1 May 2004 08:19:15 -0000 1.1.1.1
    +++ linux-2.6.6-rc3-mm1/include/asm-i386/spinlock.h 1 May 2004 18:21:41 -0000
    @@ -42,7 +42,6 @@ typedef struct {

    #define spin_is_locked(x) (*(volatile signed char *)(&(x)->lock) <= 0)
    #define spin_unlock_wait(x) do { barrier(); } while(spin_is_locked(x))
    -#define _raw_spin_lock_flags(lock, flags) _raw_spin_lock(lock)

    #ifdef CONFIG_SPINLINE

    @@ -58,6 +57,21 @@ typedef struct {
    "jmp 1b\n" \
    "3:\t"

    + #define spin_lock_string_flags \
    + "\n1:\t" \
    + "lock ; decb %0\n\t" \
    + "jns 3f\n" \
    + "testl $0x200, %1\n\t" \
    + "jz 2f\n\t" \
    + "sti\n\t" \
    + "2:\t" \
    + "rep;nop\n\t" \
    + "cmpb $0, %0\n\t" \
    + "jle 2b\n\t" \
    + "cli\n\t" \
    + "jmp 1b\n" \
    + "3:\t"
    +
    #else /* !CONFIG_SPINLINE */

    #define spin_lock_string \
    @@ -72,6 +86,26 @@ typedef struct {
    "jmp 1b\n" \
    LOCK_SECTION_END

    + #define spin_lock_string_flags \
    + "\n1:\t" \
    + "lock ; decb %0\n\t" \
    + "jns 4f\n" \
    + "testl $0x200, %1\n\t" \
    + "jz 2f\n\t" \
    + "sti\n\t" \
    + "jmp 2f\n\t" \
    + LOCK_SECTION_START("") \
    + "2:\t" \
    + "rep;nop\n\t" \
    + "cmpb $0, %0\n\t" \
    + "jle 2b\n\t" \
    + "jmp 3f\n\t" \
    + LOCK_SECTION_END \
    + "3:\t" \
    + "cli\n\t" \
    + "jmp 1b\n" \
    + "4:\t"
    +
    #endif /* CONFIG_SPINLINE */
    /*
    * This works. Despite all the confusion.
    @@ -143,6 +177,20 @@ here:
    :"=m" (lock->lock) : : "memory");
    }

    +static inline void _raw_spin_lock_flags (spinlock_t *lock, unsigned long flags)
    +{
    +#ifdef CONFIG_DEBUG_SPINLOCK
    + __label__ here;
    +here:
    + if (unlikely(lock->magic != SPINLOCK_MAGIC)) {
    + printk("eip: %p\n", &&here);
    + BUG();
    + }
    +#endif
    + __asm__ __volatile__(
    + spin_lock_string_flags
    + :"=m" (lock->lock) : "r" (flags) : "memory");
    +}

    /*
    * Read-write spinlocks, allowing multiple readers
    -
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