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Groups > linux.kernel > #1737119
| From | Marcelo Tosatti <mtosatti@redhat.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [patch 2/3] KVM: x86: KVM_HC_RT_PRIO hypercall (host-side) |
| Date | 2017-09-22 03:10 +0200 |
| Message-ID | <uskDE-8cY-7@gated-at.bofh.it> (permalink) |
| References | <us89r-rR-15@gated-at.bofh.it> <us89s-rR-31@gated-at.bofh.it> <us9RU-1Aq-3@gated-at.bofh.it> <usa1A-1Eh-15@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Thu, Sep 21, 2017 at 03:49:33PM +0200, Paolo Bonzini wrote: > On 21/09/2017 15:32, Konrad Rzeszutek Wilk wrote: > > So the guest can change the scheduling decisions at the host level? > > And the host HAS to follow it? There is no policy override for the > > host to say - nah, not going to do it? In that case the host should not even configure the guest with this option (this is QEMU's 'enable-rt-fifo-hc' option). > > Also wouldn't the guest want to always be at SCHED_FIFO? [I am thinking > > of a guest admin who wants all the CPU resources he can get] No. Because in the following code, executed by the housekeeping vCPU running at constant SCHED_FIFO priority: 1. Start disk I/O. 2. busy spin With the emulator thread sharing the same pCPU with the housekeeping vCPU, the emulator thread (which runs at SCHED_NORMAL), will never be scheduled in in place of the vcpu thread at SCHED_FIFO. This causes a hang. > Yeah, I do not understand why there should be a housekeeping VCPU that > is running at SCHED_NORMAL. If it hurts, don't do it... Hope explanation above makes sense (in fact, it was you who pointed out SCHED_FIFO should not be constant on the housekeeping vCPU, when sharing pCPU with emulator thread at SCHED_NORMAL).
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[patch 2/3] KVM: x86: KVM_HC_RT_PRIO hypercall (host-side) Marcelo Tosatti <mtosatti@redhat.com> - 2017-09-21 13:50 +0200
Re: [patch 2/3] KVM: x86: KVM_HC_RT_PRIO hypercall (host-side) Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> - 2017-09-21 15:40 +0200
Re: [patch 2/3] KVM: x86: KVM_HC_RT_PRIO hypercall (host-side) Paolo Bonzini <pbonzini@redhat.com> - 2017-09-21 15:50 +0200
Re: [patch 2/3] KVM: x86: KVM_HC_RT_PRIO hypercall (host-side) Marcelo Tosatti <mtosatti@redhat.com> - 2017-09-22 03:10 +0200
Re: [patch 2/3] KVM: x86: KVM_HC_RT_PRIO hypercall (host-side) Paolo Bonzini <pbonzini@redhat.com> - 2017-09-22 09:30 +0200
Re: [patch 2/3] KVM: x86: KVM_HC_RT_PRIO hypercall (host-side) Marcelo Tosatti <mtosatti@redhat.com> - 2017-09-22 14:30 +0200
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