Messages in this thread | | | Date | Wed, 19 Feb 2014 14:24:49 -0500 | From | Waiman Long <> | Subject | Re: [PATCH v4 0/3] qspinlock: Introducing a 4-byte queue spinlock |
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On 02/19/2014 03:51 AM, Peter Zijlstra wrote: > On Tue, Feb 18, 2014 at 07:42:20PM -0500, Waiman Long wrote: >> On 02/18/2014 04:28 PM, Peter Zijlstra wrote: >>> On Tue, Feb 18, 2014 at 02:30:12PM -0500, Waiman Long wrote: >>>> I will start looking at how to make it work with paravirt. Hopefully, it >>>> won't take too long. >>> The cheap way out is to simply switch to the test-and-set spinlock on >>> whatever X86_FEATURE_ indicates a guest I suppose. >> I don't think there is X86_FEATURE flag that indicates running in a guest. >> In fact, a guest should never find out if it is running virtualized. > No it very much should; how else is paravirt ever going to work?
We do have a CONFIG_PARAVIRT macro that turns on or off PV support. The queue spinlock can be easily changed into an unfair lock which allows lock stealing. We could have a config option to make it unfair in the PARAVIRT environment, but I don't think Linus like the idea of an unfair lock.
-Longman
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