Messages in this thread | | | Date | Mon, 14 Sep 2015 16:10:12 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v6 6/6] locking/pvqspinlock: Queue node adaptive spinning |
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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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