Re: [PATCH v6 6/6] locking/pvqspinlock: Queue node adaptive spinning

From	Waiman Long <waiman.long@hpe.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v6 6/6] locking/pvqspinlock: Queue node adaptive spinning
Date	2015-09-15 17:40 +0200
Message-ID	<q90uR-xv-3@gated-at.bofh.it> (permalink)
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On 09/15/2015 04:38 AM, Peter Zijlstra wrote:
> On Mon, Sep 14, 2015 at 03:37:32PM -0400, Waiman Long wrote:
>> BTW, the queue head vCPU at pv_wait_head_and_lock() doesn't wait early, it
>> will spin the full threshold as there is no way for it to figure out if the
>> lock holder is running or not.
> We can know its cpu id, right? Surely we should then be able to figure
> out if its active or not, I'm thinking the KVM/Xen know these things
> somewhere.

We can make a guess of the lock holder cpu id by peeking at previous MCS 
node. However, if the current lock holder got the lock without entering 
the queue or it got the lock by stealing, we won't have information of 
what CPU it is.

Cheers,
Longman
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Thread

[PATCH v6 6/6] locking/pvqspinlock: Queue node adaptive spinning Waiman Long <Waiman.Long@hpe.com> - 2015-09-11 20:40 +0200
  Re: [PATCH v6 6/6] locking/pvqspinlock: Queue node adaptive spinning Peter Zijlstra <peterz@infradead.org> - 2015-09-14 16:20 +0200
    Re: [PATCH v6 6/6] locking/pvqspinlock: Queue node adaptive spinning Waiman Long <waiman.long@hpe.com> - 2015-09-14 21:40 +0200
      Re: [PATCH v6 6/6] locking/pvqspinlock: Queue node adaptive spinning Peter Zijlstra <peterz@infradead.org> - 2015-09-15 10:40 +0200
        Re: [PATCH v6 6/6] locking/pvqspinlock: Queue node adaptive spinning Waiman Long <waiman.long@hpe.com> - 2015-09-15 17:40 +0200
          Re: [PATCH v6 6/6] locking/pvqspinlock: Queue node adaptive spinning Peter Zijlstra <peterz@infradead.org> - 2015-09-16 17:10 +0200

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