• Jason Low's avatar
    locking/spinlocks/mcs: Convert osq lock to atomic_t to reduce overhead · 90631822
    Jason Low authored
    The cancellable MCS spinlock is currently used to queue threads that are
    doing optimistic spinning. It uses per-cpu nodes, where a thread obtaining
    the lock would access and queue the local node corresponding to the CPU that
    it's running on. Currently, the cancellable MCS lock is implemented by using
    pointers to these nodes.
    
    In this patch, instead of operating on pointers to the per-cpu nodes, we
    store the CPU numbers in which the per-cpu nodes correspond to in atomic_t.
    A similar concept is used with the qspinlock.
    
    By operating on the CPU # of the nodes using atomic_t instead of pointers
    to those nodes, this can reduce the overhead of the cancellable MCS spinlock
    by 32 bits (on 64 bit systems).
    Signed-off-by: default avatarJason Low <jason.low2@hp.com>
    Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
    Cc: Scott Norton <scott.norton@hp.com>
    Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
    Cc: Dave Chinner <david@fromorbit.com>
    Cc: Waiman Long <waiman.long@hp.com>
    Cc: Davidlohr Bueso <davidlohr@hp.com>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Tim Chen <tim.c.chen@linux.intel.com>
    Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
    Cc: Aswin Chandramouleeswaran <aswin@hp.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Chris Mason <clm@fb.com>
    Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
    Cc: Josef Bacik <jbacik@fusionio.com>
    Link: http://lkml.kernel.org/r/1405358872-3732-3-git-send-email-jason.low2@hp.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    90631822
mcs_spinlock.h 3.75 KB