On Thu, Apr 09, 2015 at 09:16:24AM -0400, Rik van Riel wrote: > On 04/09/2015 03:01 AM, Peter Zijlstra wrote: > > On Wed, Apr 08, 2015 at 02:32:19PM -0400, Waiman Long wrote: > >> For a virtual guest with the qspinlock patch, a simple unfair byte lock > >> will be used if PV spinlock is not configured in or the hypervisor > >> isn't either KVM or Xen. The byte lock works fine with small guest > >> of just a few vCPUs. On a much larger guest, however, byte lock can > >> have serious performance problem. > > > > Who cares? > > There are some people out there running guests with dozens > of vCPUs. If the code exists to make those setups run better, > is there a good reason not to use it? Well use paravirt, !paravirt stuff sucks performance wise anyhow. The question really is: is the added complexity worth the maintenance burden. And I'm just not convinced !paravirt virt is a performance critical target. > Having said that, only KVM and Xen seem to support very > large guests, and PV spinlock is available there. > > I believe both VMware and Hyperv have a 32 VCPU limit, anyway. Don't we have Hyperv paravirt drivers? They could add support for paravirt spinlocks too. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
