Re: [Xen-devel] [PATCH v11 14/16] pvqspinlock: Add qspinlock para-virtualization support

[Peter Zijlstra <peterz@xxxxxxxxxxxxx>]

On Thu, Jun 12, 2014 at 04:48:41PM -0400, Waiman Long wrote:
> I don't have a good understanding of the kernel alternatives mechanism.

I didn't either; I do now, cost me a whole day reading up on
alternative/paravirt code patching.

See the patches I just send out; I got the 'native' case with paravirt
enabled to be one NOP worse than the native case without paravirt -- for
queue_spin_unlock.

The lock slowpath is several nops and some pointless movs more expensive.

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