• Waiman Long's avatar
    locking/pvqspinlock: Only kick CPU at unlock time · 75d22702
    Waiman Long authored
    
    
    For an over-committed guest with more vCPUs than physical CPUs
    available, it is possible that a vCPU may be kicked twice before
    getting the lock - once before it becomes queue head and once again
    before it gets the lock. All these CPU kicking and halting (VMEXIT)
    can be expensive and slow down system performance.
    
    This patch adds a new vCPU state (vcpu_hashed) which enables the code
    to delay CPU kicking until at unlock time. Once this state is set,
    the new lock holder will set _Q_SLOW_VAL and fill in the hash table
    on behalf of the halted queue head vCPU. The original vcpu_halted
    state will be used by pv_wait_node() only to differentiate other
    queue nodes from the qeue head.
    Signed-off-by: default avatarWaiman Long <Waiman.Long@hp.com>
    Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Douglas Hatch <doug.hatch@hp.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Scott J Norton <scott.norton@hp.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Link: http://lkml.kernel.org/r/1436647018-49734-2-git-send-email-Waiman.Long@hp.com
    
    Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
    75d22702
qspinlock.c 12.2 KB