On 01/12/14 15:05, Luis R. Rodriguez wrote: > On Mon, Dec 01, 2014 at 11:11:43AM +0000, David Vrabel wrote: >> On 27/11/14 18:36, Luis R. Rodriguez wrote: >>> On Thu, Nov 27, 2014 at 07:36:31AM +0100, Juergen Gross wrote: >>>> On 11/26/2014 11:26 PM, Luis R. Rodriguez wrote: >>>>> From: "Luis R. Rodriguez" <mcgrof@xxxxxxxx> >>>>> >>>>> Some folks had reported that some xen hypercalls take a long time >>>>> to complete when issued from the userspace private ioctl mechanism, >>>>> this can happen for instance with some hypercalls that have many >>>>> sub-operations, this can happen for instance on hypercalls that use >> [...] >>>>> --- a/drivers/xen/privcmd.c >>>>> +++ b/drivers/xen/privcmd.c >>>>> @@ -60,6 +60,9 @@ static long privcmd_ioctl_hypercall(void __user *udata) >>>>> hypercall.arg[0], hypercall.arg[1], >>>>> hypercall.arg[2], hypercall.arg[3], >>>>> hypercall.arg[4]); >>>>> +#ifndef CONFIG_PREEMPT >>>>> + schedule(); >>>>> +#endif >> >> As Juergen points out, this does nothing. You need to schedule while in >> the middle of the hypercall. >> >> Remember that Xen's hypercall preemption only preempts the hypercall to >> run interrupts in the guest. > > How is it ensured that when the kernel preempts on this code path on > CONFIG_PREEMPT=n kernel that only interrupts in the guest are run? Sorry, I really didn't describe this very well. If a hypercall needs a continuation, Xen returns to the guest with the IP set to the hypercall instruction, and on the way back to the guest Xen may schedule a different VCPU or it will do any upcalls (as per normal). The guest is free to return from the upcall to the original task (continuing the hypercall) or to a different one. David -- 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
