From: Wanpeng Li <kernellwp@gmail.com>
To: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
kvm <kvm@vger.kernel.org>,
Yunhong Jiang <yunhong.jiang@intel.com>,
Wanpeng Li <wanpeng.li@hotmail.com>
Subject: Re: [PATCH 6/5] KVM: x86: fix periodic lapic timer with hrtimers
Date: Thu, 27 Oct 2016 10:33:51 +0800 [thread overview]
Message-ID: <CANRm+CzFxyeVYMwq_+eZkCVc3ZdmC+kV2tdkyD1H_0XWO0yX9A@mail.gmail.com> (raw)
In-Reply-To: <20161026140109.GB3452@potion>
2016-10-26 22:01 GMT+08:00 Radim Krčmář <rkrcmar@redhat.com>:
> 2016-10-26 14:08+0800, Wanpeng Li:
>> 2016-10-26 14:02 GMT+08:00 Wanpeng Li <kernellwp@gmail.com>:
>>> 2016-10-25 19:43 GMT+08:00 Radim Krčmář <rkrcmar@redhat.com>:
>>>> I will have some comments, because it would be nicer if it measured the
>>>> latency ... expected_expiration is not computed correctly.
>>>
>>> It measured the latency from guest programs the clock event device to
>>> interrupt injected to guest after timer fire.
>
> No. It never computed the time when the timer fires, the test measured
> the duration of the period.
>
> Imagine that the dashed line below is a timeline. Pipe is idealized
> firing of the periodic timer and caret is the time when the guest read
> time in the interrupt. The number below caret is the latency.
>
> The period is 7.
>
> --------------------------------------------
> | | | | | | |
> ^ ^ ^ ^ ^ ^ ^
> 1 2 3 1 2 1 1
>
> The test would report "latencies" as:
>
> 1 1 1 -2 1 -1 0
>
> because it used now() + period to compute the next expected expiration
>
> Similarly in this case,
> --------------------------------------------
> | | | | | | |
> ^ ^ ^ ^ ^ ^
> 6 6 6 6 6 6
>
> The latency is always 6, but the test would report
>
> 6 0 0 0 0 0
>
> And if we improved the latency by 1, you'd only see the difference in
> the first number. The test measured the duration of the period.
Agreed, thanks for the details. :)
Regards,
Wanpeng Li
next prev parent reply other threads:[~2016-10-27 2:33 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-24 10:23 [PATCH v3 0/5] KVM: LAPIC: Add APIC Timer periodic/oneshot mode VMX preemption timer support Wanpeng Li
2016-10-24 10:23 ` [PATCH v3 1/5] KVM: LAPIC: extract start_sw_period() to handle periodic/oneshot mode Wanpeng Li
2016-10-24 10:23 ` [PATCH v3 2/5] KVM: LAPIC: guarantee the timer is in tsc-deadline mode Wanpeng Li
2016-10-24 10:23 ` [PATCH v3 3/5] KVM: LAPIC: introduce kvm_get_lapic_target_expiration_tsc() Wanpeng Li
2016-10-24 10:23 ` [PATCH v3 4/5] KVM: LAPIC: rename start/cancel_hv_tscdeadline to start/cancel_hv_timer Wanpeng Li
2016-10-24 10:23 ` [PATCH v3 5/5] KVM: LAPIC: add APIC Timer periodic/oneshot mode VMX preemption timer support Wanpeng Li
2016-10-24 14:50 ` Radim Krčmář
2016-10-24 23:33 ` Wanpeng Li
2016-10-24 15:03 ` [PATCH 6/5] KVM: x86: fix periodic lapic timer with hrtimers Radim Krčmář
2016-10-24 15:09 ` Paolo Bonzini
2016-10-24 15:27 ` Radim Krčmář
2016-10-24 23:39 ` Wanpeng Li
2016-10-25 11:43 ` Radim Krčmář
2016-10-25 11:55 ` Paolo Bonzini
2016-10-26 6:02 ` Wanpeng Li
2016-10-26 6:08 ` Wanpeng Li
2016-10-26 14:01 ` Radim Krčmář
2016-10-27 2:33 ` Wanpeng Li [this message]
2016-10-26 13:32 ` Radim Krčmář
2016-10-27 2:11 ` Wanpeng Li
2016-10-26 10:23 ` Wanpeng Li
2016-10-26 11:15 ` Paolo Bonzini
2016-10-26 11:26 ` Wanpeng Li
[not found] ` <SG2PR02MB1550E0FF04F2614BE0E262BC80A80@SG2PR02MB1550.apcprd02.prod.outlook.com>
2016-10-25 13:03 ` Radim Krčmář
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