From: "wangyanan (Y)" <wangyanan55@huawei.com>
To: Sean Christopherson <seanjc@google.com>,
Paolo Bonzini <pbonzini@redhat.com>
Cc: Wanpeng Li <wanpengli@tencent.com>, kvm <kvm@vger.kernel.org>,
David Hildenbrand <david@redhat.com>,
"Kernel Mailing List, Linux" <linux-kernel@vger.kernel.org>,
Paul Mackerras <paulus@ozlabs.org>,
Claudio Imbrenda <imbrenda@linux.ibm.com>,
KVM ARM <kvmarm@lists.cs.columbia.edu>,
Janosch Frank <frankja@linux.ibm.com>,
Marc Zyngier <maz@kernel.org>, Joerg Roedel <joro@8bytes.org>,
Huacai Chen <chenhuacai@kernel.org>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
Jon Cargille <jcargill@google.com>,
kvm-ppc <kvm-ppc@vger.kernel.org>,
David Matlack <dmatlack@google.com>,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
Jim Mattson <jmattson@google.com>,
Cornelia Huck <cohuck@redhat.com>,
"open list:MIPS" <linux-mips@vger.kernel.org>,
Vitaly Kuznetsov <vkuznets@redhat.com>
Subject: Re: disabling halt polling broken? (was Re: [PATCH 00/14] KVM: Halt-polling fixes, cleanups and a new stat)
Date: Tue, 15 Nov 2022 11:28:56 +0800 [thread overview]
Message-ID: <32810c89-44c6-6780-9d05-e49f6b897b6e@huawei.com> (raw)
In-Reply-To: <YVIAdVxc+q2UWB+J@google.com>
Hi Sean, Paolo,
I recently also notice the behavior change of param halt_poll_ns.
Now it loses the ability to:
1) dynamically disable halt polling for all the running VMs
by `echo 0 > /sys`
2) dynamically adjust the halt polling interval for all the
running VMs by `echo * > /sys`
While in our cases, we usually use above two abilities, and
KVM_CAP_HALT_POLL is not used yet.
On 2021/9/28 1:33, Sean Christopherson wrote:
> On Mon, Sep 27, 2021, Paolo Bonzini wrote:
>> On Mon, Sep 27, 2021 at 5:17 PM Christian Borntraeger
>> <borntraeger@de.ibm.com> wrote:
>>>> So I think there are two possibilities that makes sense:
>>>>
>>>> * track what is using KVM_CAP_HALT_POLL, and make writes to halt_poll_ns follow that
>>> what about using halt_poll_ns for those VMs that did not uses KVM_CAP_HALT_POLL and the private number for those that did.
>> Yes, that's what I meant. David pointed out that doesn't allow you to
>> disable halt polling altogether, but for that you can always ask each
>> VM's userspace one by one, or just not use KVM_CAP_HALT_POLL. (Also, I
>> don't know about Google's usecase, but mine was actually more about
>> using KVM_CAP_HALT_POLL to *disable* halt polling on some VMs!).
> I kinda like the idea if special-casing halt_poll_ns=0, e.g. for testing or
> in-the-field mitigation if halt-polling is broken. It'd be trivial to support, e.g.
Do we have any plan to repost the diff as a fix?
I would be very nice that this issue can be solved.
Besides, I think we may need some Doc for users to describe
how halt_poll_ns works with KVM_CAP_HALT_POLL, like
"Documentation/virt/guest-halt-polling.rst".
> @@ -3304,19 +3304,23 @@ void kvm_vcpu_halt(struct kvm_vcpu *vcpu)
> update_halt_poll_stats(vcpu, start, poll_end, !waited);
>
> if (halt_poll_allowed) {
> + max_halt_poll_ns = vcpu->kvm->max_halt_poll_ns;
> + if (!max_halt_poll_ns || !halt_poll_ns) <------ squish the max if halt_poll_ns==0
> + max_halt_poll_ns = halt_poll_ns;
> +
Does this mean that KVM_CAP_HALT_POLL will not be able to
disable halt polling for a VM individually when halt_poll_ns !=0?
> if (!vcpu_valid_wakeup(vcpu)) {
> shrink_halt_poll_ns(vcpu);
> - } else if (vcpu->kvm->max_halt_poll_ns) {
> + } else if (max_halt_poll_ns) {
> if (halt_ns <= vcpu->halt_poll_ns)
> ;
> /* we had a long block, shrink polling */
> else if (vcpu->halt_poll_ns &&
> - halt_ns > vcpu->kvm->max_halt_poll_ns)
> + halt_ns > max_halt_poll_ns)
> shrink_halt_poll_ns(vcpu);
> /* we had a short halt and our poll time is too small */
> - else if (vcpu->halt_poll_ns < vcpu->kvm->max_halt_poll_ns &&
> - halt_ns < vcpu->kvm->max_halt_poll_ns)
> - grow_halt_poll_ns(vcpu);
> + else if (vcpu->halt_poll_ns < max_halt_poll_ns &&
> + halt_ns < max_halt_poll_ns)
> + grow_halt_poll_ns(vcpu, max_halt_poll_ns);
> } else {
> vcpu->halt_poll_ns = 0;
> }
> _______________________________________________
> kvmarm mailing list
> kvmarm@lists.cs.columbia.edu
> https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
> .
Thanks,
Yanan
next prev parent reply other threads:[~2022-11-15 3:29 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-25 0:55 [PATCH 00/14] KVM: Halt-polling fixes, cleanups and a new stat Sean Christopherson
2021-09-25 0:55 ` [PATCH 01/14] KVM: s390: Ensure kvm_arch_no_poll() is read once when blocking vCPU Sean Christopherson
2021-09-27 6:54 ` Christian Borntraeger
2021-09-25 0:55 ` [PATCH 02/14] KVM: Update halt-polling stats if and only if halt-polling was attempted Sean Christopherson
2021-09-28 18:57 ` David Matlack
2021-09-25 0:55 ` [PATCH 03/14] KVM: Refactor and document halt-polling stats update helper Sean Christopherson
2021-09-28 19:01 ` David Matlack
2021-09-25 0:55 ` [PATCH 04/14] KVM: Reconcile discrepancies in halt-polling stats Sean Christopherson
2021-09-28 21:26 ` David Matlack
2021-09-25 0:55 ` [PATCH 05/14] KVM: s390: Clear valid_wakeup in kvm_s390_handle_wait(), not in arch hook Sean Christopherson
2021-09-27 6:58 ` Christian Borntraeger
2021-09-25 0:55 ` [PATCH 06/14] KVM: Drop obsolete kvm_arch_vcpu_block_finish() Sean Christopherson
2021-09-27 6:58 ` Christian Borntraeger
2021-09-28 21:28 ` David Matlack
2021-09-25 0:55 ` [PATCH 07/14] KVM: Don't block+unblock when halt-polling is successful Sean Christopherson
2021-09-25 9:50 ` Marc Zyngier
2021-09-26 6:27 ` Paolo Bonzini
2021-09-26 9:02 ` Marc Zyngier
2021-09-27 17:28 ` Sean Christopherson
2021-09-28 9:24 ` Marc Zyngier
2021-09-28 16:21 ` Sean Christopherson
2021-09-30 9:36 ` Marc Zyngier
2021-09-25 0:55 ` [PATCH 08/14] KVM: x86: Tweak halt emulation helper names to free up kvm_vcpu_halt() Sean Christopherson
2021-09-28 21:59 ` David Matlack
2021-09-25 0:55 ` [PATCH 09/14] KVM: Rename kvm_vcpu_block() => kvm_vcpu_halt() Sean Christopherson
2021-09-27 7:06 ` Christian Borntraeger
2021-09-28 22:01 ` David Matlack
2021-09-25 0:55 ` [PATCH 10/14] KVM: Split out a kvm_vcpu_block() helper from kvm_vcpu_halt() Sean Christopherson
2021-09-27 7:41 ` Christian Borntraeger
2021-09-28 22:03 ` David Matlack
2021-09-25 0:55 ` [PATCH 11/14] KVM: stats: Add stat to detect if vcpu is currently blocking Sean Christopherson
2021-09-28 22:04 ` David Matlack
2021-09-25 0:55 ` [PATCH 12/14] KVM: Don't redo ktime_get() when calculating halt-polling stop/deadline Sean Christopherson
2021-09-28 22:08 ` David Matlack
2021-09-25 0:55 ` [PATCH 13/14] KVM: x86: Directly block (instead of "halting") UNINITIALIZED vCPUs Sean Christopherson
2021-09-28 22:12 ` David Matlack
2021-09-25 0:55 ` [PATCH 14/14] KVM: x86: Invoke kvm_vcpu_block() directly for non-HALTED wait states Sean Christopherson
2021-09-28 22:14 ` David Matlack
2021-09-27 7:22 ` disabling halt polling broken? (was Re: [PATCH 00/14] KVM: Halt-polling fixes, cleanups and a new stat) Christian Borntraeger
2021-09-27 14:59 ` Sean Christopherson
2021-09-27 15:03 ` Paolo Bonzini
2021-09-27 15:15 ` Sean Christopherson
2021-09-27 15:16 ` Christian Borntraeger
2021-09-27 16:58 ` David Matlack
2021-09-29 6:56 ` Christian Borntraeger
2021-09-27 17:24 ` Paolo Bonzini
2021-09-27 17:33 ` Sean Christopherson
2022-11-15 3:28 ` wangyanan (Y) [this message]
2022-11-16 17:19 ` David Matlack
2022-11-18 2:29 ` wangyanan (Y)
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