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    SubjectRe: [PATCH v6 6/6] locking/pvqspinlock: Queue node adaptive spinning
    On Fri, Sep 11, 2015 at 02:37:38PM -0400, Waiman Long wrote:
    > In an overcommitted guest where some vCPUs have to be halted to make
    > forward progress in other areas, it is highly likely that a vCPU later
    > in the spinlock queue will be spinning while the ones earlier in the
    > queue would have been halted. The spinning in the later vCPUs is then
    > just a waste of precious CPU cycles because they are not going to
    > get the lock soon as the earlier ones have to be woken up and take
    > their turn to get the lock.
    >
    > This patch implements an adaptive spinning mechanism where the vCPU
    > will call pv_wait() if the following conditions are true:
    >
    > 1) the vCPU has not been halted before;
    > 2) the previous vCPU is not running.

    Why 1? For the mutex adaptive stuff we only care about the lock holder
    running, right?


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