Gleb Natapov wrote on 2013-03-22:
> On Fri, Mar 22, 2013 at 08:37:22AM +0000, Zhang, Yang Z wrote:
>> Gleb Natapov wrote on 2013-03-22:
>>> On Fri, Mar 22, 2013 at 08:25:21AM +0000, Zhang, Yang Z wrote:
>>>> Gleb Natapov wrote on 2013-03-22:
>>>>> On Fri, Mar 22, 2013 at 08:05:27AM +0000, Zhang, Yang Z wrote:
>>>>>> Gleb Natapov wrote on 2013-03-22:
>>>>>>> On Fri, Mar 22, 2013 at 01:24:05PM +0800, Yang Zhang wrote:
>>>>>>>> From: Yang Zhang <yang.z.zhang@xxxxxxxxx>
>>>>>>>>
>>>>>>>> Current interrupt coalescing logci which only used by RTC has
>>>>>>>> conflict with Posted Interrupt. This patch introduces a new
>>>>>>>> mechinism to use eoi to track interrupt: When delivering an
>>>>>>>> interrupt to vcpu, the pending_eoi set to number of vcpu that
>>>>>>>> received the interrupt. And decrease it when each vcpu writing
>>>>>>>> eoi. No subsequent RTC interrupt can deliver to vcpu until all
>>>>>>>> vcpus write eoi.
>>>>>>>>
>>>>>>>> Signed-off-by: Yang Zhang <yang.z.zhang@xxxxxxxxx>
>>>>>>>> ---
>>>>>>>> virt/kvm/ioapic.c | 40
>>>>>>>> +++++++++++++++++++++++++++++++++++++++- 1 files changed, 39
>>>>>>>> insertions(+), 1 deletions(-)
>>>>>>>> diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
>>>>>>>> index c991e58..df16daf 100644
>>>>>>>> --- a/virt/kvm/ioapic.c
>>>>>>>> +++ b/virt/kvm/ioapic.c
>>>>>>>> @@ -114,6 +114,29 @@ static void rtc_irq_restore(struct kvm_ioapic
>>>>> *ioapic)
>>>>>>>> ioapic->rtc_status.pending_eoi = pending_eoi;
>>>>>>>> }
>>>>>>>> +static void rtc_irq_ack_eoi(struct kvm_vcpu *vcpu,
>>>>>>>> + struct rtc_status *rtc_status, int irq)
>>>>>>>> +{
>>>>>>>> + if (irq != RTC_GSI)
>>>>>>>> + return;
>>>>>>>> +
>>>>>>>> + if (test_and_clear_bit(vcpu->vcpu_id, rtc_status->dest_map))
>>>>>>>> + --rtc_status->pending_eoi;
>>>>>>>> +
>>>>>>>> + WARN_ON(rtc_status->pending_eoi < 0);
>>>>>>>> +}
>>>>>>>> +
>>>>>>>> +static bool rtc_irq_check(struct kvm_ioapic *ioapic, int irq)
>>>>>>>> +{
>>>>>>>> + if (irq != RTC_GSI)
>>>>>>>> + return false;
>>>>>>>> +
>>>>>>>> + if (ioapic->rtc_status.pending_eoi > 0)
>>>>>>>> + return true; /* coalesced */
>>>>>>>> +
>>>>>>>> + return false;
>>>>>>>> +}
>>>>>>>> +
>>>>>>>> static int ioapic_service(struct kvm_ioapic *ioapic, unsigned int idx)
>>>>>>>> {
>>>>>>>> union kvm_ioapic_redirect_entry *pent;
>>>>>>>> @@ -229,6 +252,7 @@ static int ioapic_deliver(struct kvm_ioapic
> *ioapic,
>>> int
>>>>>>> irq)
>>>>>>>> {
>>>>>>>> union kvm_ioapic_redirect_entry *entry = &ioapic->redirtbl[irq];
>>>>>>>> struct kvm_lapic_irq irqe;
>>>>>>>> + int ret;
>>>>>>>>
>>>>>>>> ioapic_debug("dest=%x dest_mode=%x delivery_mode=%x "
>>>>>>>> "vector=%x trig_mode=%x\n",
>>>>>>>> @@ -244,7 +268,14 @@ static int ioapic_deliver(struct kvm_ioapic
> *ioapic,
>>>>> int
>>>>>>> irq)
>>>>>>>> irqe.level = 1;
>>>>>>>> irqe.shorthand = 0;
>>>>>>>> - return kvm_irq_delivery_to_apic(ioapic->kvm, NULL, &irqe,
>>>>>>>> NULL); + if (irq == RTC_GSI) { + ret =
>>>>>>>> kvm_irq_delivery_to_apic(ioapic->kvm, NULL, &irqe,
>>>>>>>> + ioapic->rtc_status.dest_map);
>>>>>>>> + ioapic->rtc_status.pending_eoi = ret;
>>>>>>> We should track status only if IRQ_STATUS ioctl was used to inject an
>>>>>>> interrupt.
>>>>>> We already know RTC will use IRQ_STATUS ioctl. Why check it again?
>>>>>>
>>>>> QEMU does. QEMU is not the only userspace.
>>>> And this will break other userspace.
>>>>
>>> How?
>> If other userspace has the reinjection logic for RTC, but it not uses IRQ_STATUS,
> then it cannot get the right coalescing info. If it also use IRQ_STATUS to get
> coalescing info, then we don't need the IRQ_STATUS check.
>>
> If userspace does not care about irq status it does not use IRQ_STATUS
> ioctl and we should not go extra mile to provide one. Not everyone cares
> about running Windows as a guest.
I see your point. But if no windows guest running, RTC is hardly used by other guests and the overheard can be ignore.
Best regards,
Yang
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