From: Sean Christopherson <seanjc@google.com>
To: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
David Matlack <dmatlack@google.com>,
Jon Cargille <jcargill@google.com>,
Jim Mattson <jmattson@google.com>,
James Morse <james.morse@arm.com>,
Alexandru Elisei <alexandru.elisei@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
David Hildenbrand <david@redhat.com>,
Cornelia Huck <cohuck@redhat.com>,
Claudio Imbrenda <imbrenda@linux.ibm.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Joerg Roedel <joro@8bytes.org>,
linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu, linux-mips@vger.kernel.org,
kvm@vger.kernel.org, kvm-ppc@vger.kernel.org,
linux-kernel@vger.kernel.org, Jing Zhang <jingzhangos@google.com>,
Marc Zyngier <maz@kernel.org>,
Huacai Chen <chenhuacai@kernel.org>,
Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
Paul Mackerras <paulus@ozlabs.org>,
Janosch Frank <frankja@linux.ibm.com>
Subject: Re: disabling halt polling broken? (was Re: [PATCH 00/14] KVM: Halt-polling fixes, cleanups and a new stat)
Date: Mon, 27 Sep 2021 14:59:47 +0000 [thread overview]
Message-ID: <YVHcY6y1GmvGJnMg@google.com> (raw)
In-Reply-To: <03f2f5ab-e809-2ba5-bd98-3393c3b843d2@de.ibm.com>
On Mon, Sep 27, 2021, Christian Borntraeger wrote:
> While looking into this series,
>
> I realized that Davids patch
>
> commit acd05785e48c01edb2c4f4d014d28478b5f19fb5
> Author: David Matlack <dmatlack@google.com>
> AuthorDate: Fri Apr 17 15:14:46 2020 -0700
> Commit: Paolo Bonzini <pbonzini@redhat.com>
> CommitDate: Fri Apr 24 12:53:17 2020 -0400
>
> kvm: add capability for halt polling
>
> broke the possibility for an admin to disable halt polling for already running KVM guests.
> In past times doing
> echo 0 > /sys/module/kvm/parameters/halt_poll_ns
>
> stopped polling system wide.
> Now all KVM guests will use the halt_poll_ns value that was active during
> startup - even those that do not use KVM_CAP_HALT_POLL.
>
> I guess this was not intended?
Ouch. I would go so far as to say that halt_poll_ns should be a hard limit on
the capability. What about having the per-VM variable track only the capability,
and then use the module param to cap the max when doing adjustments? E.g. add
a variant of this early in the series?
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 80f78daa6b8d..f50e4e31a0cf 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1078,8 +1078,6 @@ static struct kvm *kvm_create_vm(unsigned long type)
goto out_err_no_arch_destroy_vm;
}
- kvm->max_halt_poll_ns = halt_poll_ns;
-
r = kvm_arch_init_vm(kvm, type);
if (r)
goto out_err_no_arch_destroy_vm;
@@ -3136,7 +3134,8 @@ void kvm_sigset_deactivate(struct kvm_vcpu *vcpu)
sigemptyset(¤t->real_blocked);
}
-static void grow_halt_poll_ns(struct kvm_vcpu *vcpu)
+static void grow_halt_poll_ns(struct kvm_vcpu *vcpu,
+ unsigned int max_halt_poll_ns)
{
unsigned int old, val, grow, grow_start;
@@ -3150,8 +3149,8 @@ static void grow_halt_poll_ns(struct kvm_vcpu *vcpu)
if (val < grow_start)
val = grow_start;
- if (val > vcpu->kvm->max_halt_poll_ns)
- val = vcpu->kvm->max_halt_poll_ns;
+ if (val > max_halt_poll_ns)
+ val = max_halt_poll_ns;
vcpu->halt_poll_ns = val;
out:
@@ -3261,6 +3260,7 @@ void kvm_vcpu_halt(struct kvm_vcpu *vcpu)
{
bool halt_poll_allowed = !kvm_arch_no_poll(vcpu);
bool do_halt_poll = halt_poll_allowed && vcpu->halt_poll_ns;
+ unsigned int max_halt_poll_ns;
ktime_t start, cur, poll_end;
bool waited = false;
u64 halt_ns;
@@ -3304,19 +3304,25 @@ 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)
+ max_halt_poll_ns = min(max_halt_poll_ns, halt_poll_ns);
+ else
+ max_halt_poll_ns = halt_poll_ns;
+
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;
}
next prev parent reply other threads:[~2021-09-27 15:00 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 [this message]
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)
2022-11-16 17:19 ` David Matlack
2022-11-18 2:29 ` wangyanan (Y)
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