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Groups > linux.kernel > #1737476
| From | Marcelo Tosatti <mtosatti@redhat.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall\ |
| Date | 2017-09-22 14:50 +0200 |
| Message-ID | <usvz5-68T-45@gated-at.bofh.it> (permalink) |
| References | (3 earlier) <usakW-21y-23@gated-at.bofh.it> <uskNj-8fY-5@gated-at.bofh.it> <ust4f-4Qp-39@gated-at.bofh.it> <usv61-5Zz-13@gated-at.bofh.it> <usvpo-65F-17@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Fri, Sep 22, 2017 at 02:31:07PM +0200, Peter Zijlstra wrote:
> On Fri, Sep 22, 2017 at 09:16:40AM -0300, Marcelo Tosatti wrote:
> > On Fri, Sep 22, 2017 at 12:00:05PM +0200, Peter Zijlstra wrote:
> > > On Thu, Sep 21, 2017 at 10:10:41PM -0300, Marcelo Tosatti wrote:
> > > > When executing guest vcpu-0 with FIFO:1 priority, which is necessary
> > > > to
> > > > deal with the following situation:
> > > >
> > > > VCPU-0 (housekeeping VCPU) VCPU-1 (realtime VCPU)
> > > >
> > > > raw_spin_lock(A)
> > > > interrupted, schedule task T-1 raw_spin_lock(A) (spin)
> > > >
> > > > raw_spin_unlock(A)
> > > >
> > > > Certain operations must interrupt guest vcpu-0 (see trace below).
> > >
> > > Those traces don't make any sense. All they include is kvm_exit and you
> > > can't tell anything from that.
> >
> > Hi Peter,
> >
> > OK lets describe whats happening:
> >
> > With QEMU emulator thread and vcpu-0 sharing a physical CPU
> > (which is a request from several NFV customers, to improve
> > guest packing), the following occurs when the guest generates
> > the following pattern:
> >
> > 1. submit IO.
> > 2. busy spin.
>
> User-space spinning is a bad idea in general and terminally broken in
> a RT setup. Sounds like you need to go fix qemu to not suck.
Are you arguing its invalid for the following application to execute on
housekeeping vcpu of a realtime system:
void main(void)
{
submit_IO();
do {
computation();
} while (!interrupted());
}
Really?
Replace "busy spin" by "useful computation until interrupted".
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[patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall Marcelo Tosatti <mtosatti@redhat.com> - 2017-09-21 13:50 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> - 2017-09-21 15:40 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall Peter Zijlstra <peterz@infradead.org> - 2017-09-21 16:10 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall Marcelo Tosatti <mtosatti@redhat.com> - 2017-09-22 03:20 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall Peter Zijlstra <peterz@infradead.org> - 2017-09-22 12:10 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall Peter Zijlstra <peterz@infradead.org> - 2017-09-22 13:00 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall Marcelo Tosatti <mtosatti@redhat.com> - 2017-09-22 14:40 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall Peter Zijlstra <peterz@infradead.org> - 2017-09-22 15:00 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall Paolo Bonzini <pbonzini@redhat.com> - 2017-09-23 13:00 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall Peter Zijlstra <peterz@infradead.org> - 2017-09-23 15:50 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall Paolo Bonzini <pbonzini@redhat.com> - 2017-09-24 15:10 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall Marcelo Tosatti <mtosatti@redhat.com> - 2017-09-25 05:00 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall Peter Zijlstra <peterz@infradead.org> - 2017-09-25 11:20 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall Paolo Bonzini <pbonzini@redhat.com> - 2017-09-25 17:20 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> - 2017-09-25 18:30 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall Marcelo Tosatti <mtosatti@redhat.com> - 2017-09-22 14:20 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall Peter Zijlstra <peterz@infradead.org> - 2017-09-22 14:40 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall Marcelo Tosatti <mtosatti@redhat.com> - 2017-09-22 14:40 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall Peter Zijlstra <peterz@infradead.org> - 2017-09-22 15:10 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall Marcelo Tosatti <mtosatti@redhat.com> - 2017-09-25 04:30 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall Peter Zijlstra <peterz@infradead.org> - 2017-09-25 10:40 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall\ Marcelo Tosatti <mtosatti@redhat.com> - 2017-09-22 14:50 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall\ Peter Zijlstra <peterz@infradead.org> - 2017-09-22 15:10 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall\ Marcelo Tosatti <mtosatti@redhat.com> - 2017-09-25 04:30 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall\ Peter Zijlstra <peterz@infradead.org> - 2017-09-25 11:00 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall\ Thomas Gleixner <tglx@linutronix.de> - 2017-09-25 12:50 +0200
Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall\ Jan Kiszka <jan.kiszka@siemens.com> - 2017-09-25 20:40 +0200
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