• Waiman Long's avatar
    locking/lockdep: Make class->ops a percpu counter and move it under CONFIG_DEBUG_LOCKDEP=y · 8ca2b56c
    Waiman Long authored
    A sizable portion of the CPU cycles spent on the __lock_acquire() is used
    up by the atomic increment of the class->ops stat counter. By taking it out
    from the lock_class structure and changing it to a per-cpu per-lock-class
    counter, we can reduce the amount of cacheline contention on the class
    structure when multiple CPUs are trying to acquire locks of the same
    class simultaneously.
    
    To limit the increase in memory consumption because of the percpu nature
    of that counter, it is now put back under the CONFIG_DEBUG_LOCKDEP
    config option. So the memory consumption increase will only occur if
    CONFIG_DEBUG_LOCKDEP is defined. The lock_class structure, however,
    is reduced in size by 16 bytes on 64-bit archs after ops removal and
    a minor restructuring of the fields.
    
    This patch also fixes a bug in the increment code as the counter is of
    the 'unsigned long' type, but atomic_inc() was used to increment it.
    Signed-off-by: Waiman Long's avatarWaiman Long <longman@redhat.com>
    Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Will Deacon <will.deacon@arm.com>
    Link: http://lkml.kernel.org/r/d66681f3-8781-9793-1dcf-2436a284550b@redhat.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    8ca2b56c
lockdep.h 18.4 KB