• Chuck Ebbert's avatar
    [PATCH] i386 spinlocks: disable interrupts only if we enabled them · 42c059e0
    Chuck Ebbert authored
    _raw_spin_lock_flags() is entered with interrupts disabled.  If it cannot
    obtain a spinlock, it checks the flags that were passed and re-enables
    interrupts before spinning if that's how the flags are set.  When the
    spinlock might be available, it disables interrupts (even if they are
    already disabled) before trying to get the lock.  Change that so interrupts
    are only disabled if they have been enabled.  This costs nine bytes of
    duplicated spinloop code.
    
    Fastpath before patch:
            jle <keep looping>      not-taken conditional jump
            cli                     disable interrupts
            jmp <try for lock>      unconditional jump
    
    Fastpath after patch, if interrupts were not enabled:
            jg <try for lock>       taken conditional branch
    Signed-off-by: default avatarChuck Ebbert <76306.1226@compuserve.com>
    Acked-by: default avatarIngo Molnar <mingo@elte.hu>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
    42c059e0
spinlock.h 4.34 KB