From: David Matlack <dmatlack@google.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Marc Zyngier <maz@kernel.org>,
Huacai Chen <chenhuacai@kernel.org>,
Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
Paul Mackerras <paulus@ozlabs.org>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Janosch Frank <frankja@linux.ibm.com>,
Paolo Bonzini <pbonzini@redhat.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>,
Jim Mattson <jmattson@google.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>
Subject: Re: [PATCH 04/14] KVM: Reconcile discrepancies in halt-polling stats
Date: Tue, 28 Sep 2021 21:26:13 +0000 [thread overview]
Message-ID: <YVOIdZhAe5Bqn4hc@google.com> (raw)
In-Reply-To: <20210925005528.1145584-5-seanjc@google.com>
On Fri, Sep 24, 2021 at 05:55:18PM -0700, Sean Christopherson wrote:
> Move the halt-polling "success" and histogram stats update into the
> dedicated helper to fix a discrepancy where the success/fail "time" stats
> consider polling successful so long as the wait is avoided, but the main
> "success" and histogram stats consider polling successful if and only if
> a wake event was detected by the halt-polling loop.
>
> Move halt_attempted_poll to the helper as well so that all the stats are
> updated in a single location. While it's a bit odd to update the stat
> well after the fact, practically speaking there's no meaningful advantage
> to updating before polling.
>
> Note, there is a functional change in addition to the success vs. fail
> change. The histogram updates previously called ktime_get() instead of
> using "cur". But that change is desirable as it means all the stats are
> now updated with the same polling time, and avoids the extra ktime_get(),
> which isn't expensive but isn't free either.
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: David Matlack <dmatlack@google.com>
> ---
> virt/kvm/kvm_main.c | 35 ++++++++++++++++-------------------
> 1 file changed, 16 insertions(+), 19 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 12fe91a0a4c8..2ba22b68af3b 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -3202,12 +3202,23 @@ static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)
> static inline void update_halt_poll_stats(struct kvm_vcpu *vcpu, ktime_t start,
> ktime_t end, bool success)
> {
> + struct kvm_vcpu_stat_generic *stats = &vcpu->stat.generic;
> u64 poll_ns = ktime_to_ns(ktime_sub(end, start));
>
> - if (success)
> - vcpu->stat.generic.halt_poll_success_ns += poll_ns;
> - else
> - vcpu->stat.generic.halt_poll_fail_ns += poll_ns;
> + ++vcpu->stat.generic.halt_attempted_poll;
> +
> + if (success) {
> + ++vcpu->stat.generic.halt_successful_poll;
> +
> + if (!vcpu_valid_wakeup(vcpu))
> + ++vcpu->stat.generic.halt_poll_invalid;
> +
> + stats->halt_poll_success_ns += poll_ns;
> + KVM_STATS_LOG_HIST_UPDATE(stats->halt_poll_success_hist, poll_ns);
> + } else {
> + stats->halt_poll_fail_ns += poll_ns;
> + KVM_STATS_LOG_HIST_UPDATE(stats->halt_poll_fail_hist, poll_ns);
> + }
> }
>
> /*
> @@ -3227,30 +3238,16 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
> if (do_halt_poll) {
> ktime_t stop = ktime_add_ns(ktime_get(), vcpu->halt_poll_ns);
>
> - ++vcpu->stat.generic.halt_attempted_poll;
> do {
> /*
> * This sets KVM_REQ_UNHALT if an interrupt
> * arrives.
> */
> - if (kvm_vcpu_check_block(vcpu) < 0) {
> - ++vcpu->stat.generic.halt_successful_poll;
> - if (!vcpu_valid_wakeup(vcpu))
> - ++vcpu->stat.generic.halt_poll_invalid;
> -
> - KVM_STATS_LOG_HIST_UPDATE(
> - vcpu->stat.generic.halt_poll_success_hist,
> - ktime_to_ns(ktime_get()) -
> - ktime_to_ns(start));
> + if (kvm_vcpu_check_block(vcpu) < 0)
> goto out;
> - }
> cpu_relax();
> poll_end = cur = ktime_get();
> } while (kvm_vcpu_can_poll(cur, stop));
> -
> - KVM_STATS_LOG_HIST_UPDATE(
> - vcpu->stat.generic.halt_poll_fail_hist,
> - ktime_to_ns(ktime_get()) - ktime_to_ns(start));
> }
>
>
> --
> 2.33.0.685.g46640cef36-goog
>
next prev parent reply other threads:[~2021-09-28 21:26 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 [this message]
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)
2022-11-16 17:19 ` David Matlack
2022-11-18 2:29 ` wangyanan (Y)
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