Messages in this thread | | | Date | Fri, 30 Sep 2016 02:58:58 -0400 (EDT) | From | Paolo Bonzini <> | Subject | Re: [PATCH v3 0/4] implement vcpu preempted check |
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> > > > Please consider s390 and (x86/arm) KVM. Once we have a few, more can > > > > follow later, but I think its important to not only have PPC support for > > > > this. > > > > > > Actually the s390 preemted check via sigp sense running is available for > > > all hypervisors (z/VM, LPAR and KVM) which implies everywhere as you can > > > no longer buy s390 systems without LPAR. > > > > > > As Heiko already pointed out we could simply use a small inline function > > > that calls cpu_is_preempted from arch/s390/lib/spinlock (or > > > smp_vcpu_scheduled from smp.c) > > > > Sure, and I had vague memories of Heiko's email. This patch set however > > completely fails to do that trivial hooking up. > > sorry for that. > I will try to work it out on x86.
x86 has no hypervisor support, and I'd like to understand the desired semantics first, so I don't think it should block this series. In particular, there are at least the following choices:
1) exit to userspace (5-10.000 clock cycles best case) counts as lock holder preemption
2) any time the vCPU thread not running counts as lock holder preemption
To implement the latter you'd need a hypercall or MSR (at least as a slow path), because the KVM preempt notifier is only active during the KVM_RUN ioctl.
Paolo
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