From: Marcelo Tosatti <mtosatti@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
mingo@redhat.com, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall\
Date: Fri, 29 Sep 2017 13:40:06 -0300 [thread overview]
Message-ID: <20170929164006.GC29391@amt.cnet> (raw)
In-Reply-To: <06b714d8-7b66-6e03-a992-e359241abf84@redhat.com>
On Fri, Sep 29, 2017 at 10:18:25AM +0200, Paolo Bonzini wrote:
> On 28/09/2017 23:35, Marcelo Tosatti wrote:
> > On Thu, Sep 28, 2017 at 09:22:02AM +0200, Paolo Bonzini wrote:
> >> On 28/09/2017 02:44, Marcelo Tosatti wrote:
> >>>> Again: if you have many interruptions, it's not a flaw in KVM or QEMU's
> >>>> design, it's just that someone is doing something stupid. It could be
> >>>> the guest (e.g. unnecessary devices or daemons as in the example above),
> >>>> QEMU (e.g. the RTC emulation used to trigger QEMU timers twice a second
> >>>> just to increment the clock), or the management (e.g. polling "is the VM
> >>>> running" 50 times per second). But it can and must be fixed.
> >>>
> >>> No, i mean you can run anything in VCPU-0 (it is valid to do that).
> >>> And that "anything" can generate 1 interrupt per second, 1000 or 10.000
> >>> interrupts per second. Which are all valid things to be done.
> >>>
> >>> "I can't run a kernel compilation on VCPU-0 because that will impact
> >>> latency on the realtime VCPU-1" is not acceptable.
> >>
> >> That shouldn't happen. Sources of frequent interruptions have all been
> >> fixed or moved outside the main thread.
> >>
> >> If there are more left, report the bug and we'll see how to fix it in
> >> userspace.
> >
> > What should not happen? The generation of 10.000 interrupts per second
> > (say disk IO completion) on a given workload ?
>
> If you know you have this kind disk workload, you must use virtio-blk or
> virtio-scsi with iothreads and place the iothreads on their own physical
> CPUs.
>
> Among "run arbitrary workloads", "run real-time workloads", "pack stuff
> into as few physical CPUs as possible", you can only pick two.
>
> Paolo
Thats not the state of things (userspace in vcpu-0 is not specially tailored
to not violate latencies in vcpu-1): that is not all user triggered
actions can be verified.
Think "updatedb", and so on...
next prev parent reply other threads:[~2017-09-29 16:40 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
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 [this message]
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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