Re: [PATCH v3 0/4] implement vcpu preempted check

From	Paolo Bonzini <pbonzini@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v3 0/4] implement vcpu preempted check
Date	2016-09-30 09:10 +0200
Message-ID	<sn07f-73F-1@gated-at.bofh.it> (permalink)
References	<rXgU1-4ur-7@gated-at.bofh.it> <smGBz-2K0-7@gated-at.bofh.it> <smGLh-2Ok-59@gated-at.bofh.it> <smGUV-2TV-3@gated-at.bofh.it> <smYf7-5TN-1@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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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

Thread

Re: [PATCH v3 0/4] implement vcpu preempted check Peter Zijlstra <peterz@infradead.org> - 2016-09-29 12:20 +0200
  Re: [PATCH v3 0/4] implement vcpu preempted check Christian Borntraeger <borntraeger@de.ibm.com> - 2016-09-29 12:30 +0200
    Re: [PATCH v3 0/4] implement vcpu preempted check Peter Zijlstra <peterz@infradead.org> - 2016-09-29 12:40 +0200
      Re: [PATCH v3 0/4] implement vcpu preempted check Pan Xinhui <xinhui@linux.vnet.ibm.com> - 2016-09-30 07:10 +0200
        Re: [PATCH v3 0/4] implement vcpu preempted check Paolo Bonzini <pbonzini@redhat.com> - 2016-09-30 09:10 +0200
          Re: [PATCH v3 0/4] implement vcpu preempted check Pan Xinhui <xinhui@linux.vnet.ibm.com> - 2016-09-30 11:00 +0200
            Re: [PATCH v3 0/4] implement vcpu preempted check Paolo Bonzini <pbonzini@redhat.com> - 2016-09-30 11:10 +0200
              Re: [PATCH v3 0/4] implement vcpu preempted check Pan Xinhui <xinhui@linux.vnet.ibm.com> - 2016-09-30 11:40 +0200
          Re: [PATCH v3 0/4] implement vcpu preempted check Christian Borntraeger <borntraeger@de.ibm.com> - 2016-09-30 12:50 +0200
    Re: [PATCH v3 0/4] implement vcpu preempted check Christian Borntraeger <borntraeger@de.ibm.com> - 2016-09-29 12:50 +0200
      Re: [PATCH v3 0/4] implement vcpu preempted check Christian Borntraeger <borntraeger@de.ibm.com> - 2016-09-29 13:10 +0200

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