On 02/11/2017 19:08, Eduardo Valentin wrote: > On Thu, Nov 02, 2017 at 06:56:46PM +0100, Paolo Bonzini wrote: >> On 02/11/2017 18:45, Eduardo Valentin wrote: >>> Currently, the existing qspinlock implementation will fallback to >>> test-and-set if the hypervisor has not set the PV_UNHALT flag. >>> >>> This patch gives the opportunity to guest kernels to select >>> between test-and-set and the regular queueu fair lock implementation >>> based on the PV_DEDICATED KVM feature flag. When the PV_DEDICATED >>> flag is not set, the code will still fall back to test-and-set, >>> but when the PV_DEDICATED flag is set, the code will use >>> the regular queue spinlock implementation. >> >> Have you seen Waiman's series that lets you specify this on the guest >> command line instead? Would this be acceptable for your use case? > > No, can you please share a link to it? is it already merged to tip/master? [PATCH-tip v2 0/2] x86/paravirt: Enable users to choose PV lock type https://lkml.org/lkml/2017/11/1/655 >> (In other words, is there a difference for you between making the host >> vs. guest administrator toggle the feature? "@amazon.com" means you are >> the host admin, how would you use it?) > > The way I think of this is this is a flag set by host side so the > guest adapts accordingly. > > If the admin in guest side wants to ignore what the host is > flagging, that is a different story. Okay, this makes sense. But perhaps it should be a separate CPUID leaf, such as "configuration hints", rather than properly a feature. Paolo
