On Wed, Feb 19, 2014 at 02:24:49PM -0500, Waiman Long wrote: > 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. No; a guest is very much aware of paravirt. See for example the static_key_false(¶virt_ticketlocks_enabled). It would be impossible to set that branch if you never knew you were a guest. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
