From: Marcelo Tosatti <mtosatti@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [patch 2/3] KVM: x86: KVM_HC_RT_PRIO hypercall (host-side)
Date: Thu, 21 Sep 2017 22:08:13 -0300 [thread overview]
Message-ID: <20170922010811.GA20133@amt.cnet> (raw)
In-Reply-To: <a81e4091-6d00-141b-7f3c-3331b0f34892@redhat.com>
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).
next prev parent reply other threads:[~2017-09-22 1:08 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-21 11:38 [patch 0/3] KVM KVM_HC_RT_PRIO hypercall support Marcelo Tosatti
2017-09-21 11:38 ` [patch 1/3] KVM: x86: add per-vcpu option to set guest vcpu -RT priority Marcelo Tosatti
2017-09-21 11:38 ` [patch 2/3] KVM: x86: KVM_HC_RT_PRIO hypercall (host-side) Marcelo Tosatti
2017-09-21 13:32 ` Konrad Rzeszutek Wilk
2017-09-21 13:49 ` Paolo Bonzini
2017-09-22 1:08 ` Marcelo Tosatti [this message]
2017-09-22 7:23 ` Paolo Bonzini
2017-09-22 12:24 ` Marcelo Tosatti
2017-09-21 11:38 ` [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall Marcelo Tosatti
2017-09-21 13:36 ` Konrad Rzeszutek Wilk
2017-09-21 14:06 ` Peter Zijlstra
2017-09-22 1:10 ` Marcelo Tosatti
2017-09-22 10:00 ` Peter Zijlstra
2017-09-22 10:56 ` Peter Zijlstra
2017-09-22 12:33 ` Marcelo Tosatti
2017-09-22 12:55 ` Peter Zijlstra
2017-09-23 10:56 ` Paolo Bonzini
2017-09-23 13:41 ` Peter Zijlstra
2017-09-24 13:05 ` Paolo Bonzini
2017-09-25 2:57 ` Marcelo Tosatti
2017-09-25 9:13 ` Peter Zijlstra
2017-09-25 15:12 ` Paolo Bonzini
2017-09-26 22:49 ` [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall\ Marcelo Tosatti
2017-09-27 9:37 ` Paolo Bonzini
2017-09-28 0:44 ` Marcelo Tosatti
2017-09-28 7:22 ` Paolo Bonzini
2017-09-28 21:35 ` Marcelo Tosatti
2017-09-28 21:41 ` Marcelo Tosatti
2017-09-29 8:18 ` Paolo Bonzini
2017-09-29 16:40 ` Marcelo Tosatti
2017-09-29 17:05 ` Paolo Bonzini
2017-09-29 20:17 ` Marcelo Tosatti
2017-10-02 12:30 ` Paolo Bonzini
2017-10-02 12:48 ` Peter Zijlstra
2017-09-26 23:22 ` [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall Marcelo Tosatti
2017-09-25 16:20 ` Konrad Rzeszutek Wilk
2017-09-22 12:16 ` Marcelo Tosatti
2017-09-22 12:31 ` Peter Zijlstra
2017-09-22 12:36 ` Marcelo Tosatti
2017-09-22 12:59 ` Peter Zijlstra
2017-09-25 1:52 ` Marcelo Tosatti
2017-09-25 8:35 ` Peter Zijlstra
2017-09-22 12:40 ` [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall\ Marcelo Tosatti
2017-09-22 13:01 ` Peter Zijlstra
2017-09-25 2:22 ` Marcelo Tosatti
2017-09-25 8:58 ` Peter Zijlstra
2017-09-25 10:41 ` Thomas Gleixner
2017-09-25 18:28 ` Jan Kiszka
2017-09-21 17:45 ` [patch 0/3] KVM KVM_HC_RT_PRIO hypercall support Jan Kiszka
2017-09-22 1:19 ` Marcelo Tosatti
2017-09-22 6:23 ` Jan Kiszka
2017-09-26 23:59 ` Marcelo Tosatti
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