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From: Paolo Bonzini <pbonzini@redhat.com>
To: Roman Kagan <rkagan@virtuozzo.com>,
	Andrey Smetanin <asmetanin@virtuozzo.com>,
	kvm@vger.kernel.org, Gleb Natapov <gleb@kernel.org>,
	"K. Y. Srinivasan" <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	"Denis V. Lunev" <den@openvz.org>,
	qemu-devel@nongnu.org
Subject: Re: [PATCH v1 7/7] kvm/x86: Hyper-V SynIC timers
Date: Fri, 27 Nov 2015 11:49:40 +0100	[thread overview]
Message-ID: <56583544.3040600@redhat.com> (raw)
In-Reply-To: <20151127081244.GC2808@rkaganb.sw.ru>



On 27/11/2015 09:12, Roman Kagan wrote:
>> > +	n = div64_u64(time_now - stimer->exp_time, stimer->count) + 1;
>> > +	stimer->exp_time += n * stimer->count;
> This is actually just a reminder calculation so I'd rather do it
> directly with div64_u64_rem().

It took me a while to understand why it was a remained. :)  Expanding
Andrey's formula you get

	exp_time = exp_time + count + (time_now - exp_time) / count * count

the remainder, (time_now - exp_time) % count would be

	time_now - exp_time - (time_now - exp_time) / count * count

so -((time_now - exp_time) % count) is

	exp_time - time_now + (time_now - exp_time) / count * count

so Andrey's expression is

	exp_time = time_now + (count - (time_now - exp_time) % count)

Yeah, that looks nice.

Paolo

WARNING: multiple messages have this Message-ID (diff)
From: Paolo Bonzini <pbonzini@redhat.com>
To: Roman Kagan <rkagan@virtuozzo.com>,
	Andrey Smetanin <asmetanin@virtuozzo.com>,
	kvm@vger.kernel.org, Gleb Natapov <gleb@kernel.org>,
	"K. Y. Srinivasan" <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	"Denis V. Lunev" <den@openvz.org>,
	qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH v1 7/7] kvm/x86: Hyper-V SynIC timers
Date: Fri, 27 Nov 2015 11:49:40 +0100	[thread overview]
Message-ID: <56583544.3040600@redhat.com> (raw)
In-Reply-To: <20151127081244.GC2808@rkaganb.sw.ru>



On 27/11/2015 09:12, Roman Kagan wrote:
>> > +	n = div64_u64(time_now - stimer->exp_time, stimer->count) + 1;
>> > +	stimer->exp_time += n * stimer->count;
> This is actually just a reminder calculation so I'd rather do it
> directly with div64_u64_rem().

It took me a while to understand why it was a remained. :)  Expanding
Andrey's formula you get

	exp_time = exp_time + count + (time_now - exp_time) / count * count

the remainder, (time_now - exp_time) % count would be

	time_now - exp_time - (time_now - exp_time) / count * count

so -((time_now - exp_time) % count) is

	exp_time - time_now + (time_now - exp_time) / count * count

so Andrey's expression is

	exp_time = time_now + (count - (time_now - exp_time) % count)

Yeah, that looks nice.

Paolo

  reply	other threads:[~2015-11-27 10:49 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-11-25 15:20 [PATCH v1 0/7] KVM: Hyper-V SynIC timers Andrey Smetanin
2015-11-25 15:20 ` [Qemu-devel] " Andrey Smetanin
2015-11-25 15:20 ` [PATCH v1 1/7] drivers/hv: Move HV_SYNIC_STIMER_COUNT into Hyper-V UAPI x86 header Andrey Smetanin
2015-11-25 15:20   ` [Qemu-devel] " Andrey Smetanin
2015-11-27 17:27   ` KY Srinivasan
2015-11-27 17:27     ` [Qemu-devel] " KY Srinivasan
2015-11-25 15:20 ` [PATCH v1 2/7] drivers/hv: Move struct hv_message into UAPI Hyper-V " Andrey Smetanin
2015-11-25 15:20   ` [Qemu-devel] " Andrey Smetanin
2015-11-27  9:34   ` Paolo Bonzini
2015-11-27  9:34     ` [Qemu-devel] " Paolo Bonzini
2015-11-27 11:21     ` Andrey Smetanin
2015-11-27 11:21       ` [Qemu-devel] " Andrey Smetanin
2015-11-27 17:34     ` KY Srinivasan
2015-11-27 17:34       ` [Qemu-devel] " KY Srinivasan
2015-11-25 15:20 ` [PATCH v1 3/7] kvm/x86: Rearrange func's declarations inside Hyper-V header Andrey Smetanin
2015-11-25 15:20   ` [Qemu-devel] " Andrey Smetanin
2015-11-25 15:20 ` [PATCH v1 4/7] kvm/x86: Added Hyper-V vcpu_to_hv_vcpu()/hv_vcpu_to_vcpu() helpers Andrey Smetanin
2015-11-25 15:20   ` [Qemu-devel] " Andrey Smetanin
2015-11-25 15:20 ` [PATCH v1 5/7] kvm/x86: Hyper-V internal helper to read MSR HV_X64_MSR_TIME_REF_COUNT Andrey Smetanin
2015-11-25 15:20   ` [Qemu-devel] " Andrey Smetanin
2015-11-25 15:20 ` [PATCH v1 6/7] kvm/x86: Hyper-V SynIC message slot pending clearing at SINT ack Andrey Smetanin
2015-11-25 15:20   ` [Qemu-devel] " Andrey Smetanin
2015-11-25 16:52   ` Paolo Bonzini
2015-11-25 16:52     ` [Qemu-devel] " Paolo Bonzini
2015-11-25 16:55     ` Andrey Smetanin
2015-11-25 16:55       ` [Qemu-devel] " Andrey Smetanin
2015-11-25 17:14       ` Paolo Bonzini
2015-11-25 17:14         ` [Qemu-devel] " Paolo Bonzini
2015-11-26  9:06         ` Andrey Smetanin
2015-11-26  9:06           ` [Qemu-devel] " Andrey Smetanin
2015-11-26 14:43           ` Paolo Bonzini
2015-11-26 14:43             ` [Qemu-devel] " Paolo Bonzini
2015-11-26 15:53             ` Andrey Smetanin
2015-11-26 15:53               ` [Qemu-devel] " Andrey Smetanin
2015-11-26 15:56               ` Paolo Bonzini
2015-11-26 15:56                 ` [Qemu-devel] " Paolo Bonzini
2015-11-27  8:16   ` Roman Kagan
2015-11-27  8:16     ` [Qemu-devel] " Roman Kagan
2015-11-25 15:20 ` [PATCH v1 7/7] kvm/x86: Hyper-V SynIC timers Andrey Smetanin
2015-11-25 15:20   ` [Qemu-devel] " Andrey Smetanin
2015-11-27  8:12   ` Roman Kagan
2015-11-27  8:12     ` [Qemu-devel] " Roman Kagan
2015-11-27 10:49     ` Paolo Bonzini [this message]
2015-11-27 10:49       ` Paolo Bonzini
2015-11-27 11:24       ` Andrey Smetanin
2015-11-27 11:24         ` [Qemu-devel] " Andrey Smetanin
2015-11-30 12:17       ` Roman Kagan
2015-11-30 12:17         ` [Qemu-devel] " Roman Kagan
2015-11-26  5:28 ` [PATCH v1 0/7] KVM: " Wanpeng Li
2015-11-26  5:28   ` [Qemu-devel] " Wanpeng Li
2015-11-26  8:34   ` Andrey Smetanin
2015-11-26  8:34     ` [Qemu-devel] " Andrey Smetanin
2015-11-26  9:03     ` Wanpeng Li
2015-11-26  9:03       ` [Qemu-devel] " Wanpeng Li
2015-12-01 10:12     ` Wanpeng Li
2015-12-01 10:12       ` [Qemu-devel] " Wanpeng Li
2015-12-01 10:28       ` Denis V. Lunev
2015-12-01 10:28         ` [Qemu-devel] " Denis V. Lunev

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