> -----Original Message----- > From: Marcelo Tosatti [mailto:mtosatti@xxxxxxxxxx] > Sent: Saturday, March 28, 2015 3:30 AM > To: Wu, Feng > Cc: hpa@xxxxxxxxx; tglx@xxxxxxxxxxxxx; mingo@xxxxxxxxxx; x86@xxxxxxxxxx; > gleb@xxxxxxxxxx; pbonzini@xxxxxxxxxx; dwmw2@xxxxxxxxxxxxx; > joro@xxxxxxxxxx; alex.williamson@xxxxxxxxxx; jiang.liu@xxxxxxxxxxxxxxx; > eric.auger@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx > Subject: Re: [v3 24/26] KVM: Update Posted-Interrupts Descriptor when vCPU > is blocked > > On Fri, Mar 27, 2015 at 06:34:14AM +0000, Wu, Feng wrote: > > > > Currently, the following code is executed before local_irq_disable() is > called, > > > > so do you mean 1)moving local_irq_disable() to the place before it. 2) after > > > interrupt > > > > is disabled, set KVM_REQ_EVENT in case the ON bit is set? > > > > > > 2) after interrupt is disabled, set KVM_REQ_EVENT in case the ON bit > > > is set. > > > > Here is my understanding about your comments here: > > - Disable interrupts > > - Check 'ON' > > - Set KVM_REQ_EVENT if 'ON' is set > > > > Then we can put the above code inside " if > (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win) " > > just like it used to be. However, I still have some questions about this > comment: > > > > 1. Where should I set KVM_REQ_EVENT? In function vcpu_enter_guest(), or > other places? > > See below: > > > If in vcpu_enter_guest(), since currently local_irq_disable() is called after > 'KVM_REQ_EVENT' > > is checked, is it helpful to set KVM_REQ_EVENT after local_irq_disable() is > called? > > local_irq_disable(); > > *** add code here *** So we need add code like the following here, right? if ('ON' is set) kvm_make_request(KVM_REQ_EVENT, vcpu); > > if (vcpu->mode == EXITING_GUEST_MODE || vcpu->requests > ^^^^^^^^^^^^^^ > || need_resched() || signal_pending(current)) { > vcpu->mode = OUTSIDE_GUEST_MODE; > smp_wmb(); > local_irq_enable(); > preempt_enable(); > vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu); > r = 1; > goto cancel_injection; > } > > > 2. 'ON' is set by VT-d hardware, it can be set even when interrupt is disabled > (the related bit in PIR is also set). > > Yes, we are checking if the HW has set an interrupt in PIR while > outside VM (which requires PIR->VIRR transfer by software). > > If the interrupt it set by hardware after local_irq_disable(), > VMX-entry will handle the interrupt and perform the PIR->VIRR > transfer and reevaluate interrupts, injecting to guest > if necessary, is that correct ? > > > So does it make sense to check 'ON' and set KVM_REQ_EVENT accordingly > after interrupt is disabled? > > To replace the costly > > + */ > + if (kvm_x86_ops->hwapic_irr_update) > + kvm_x86_ops->hwapic_irr_update(vcpu, > + kvm_lapic_find_highest_irr(vcpu)); > > Yes, i think so. After adding the "checking ON and setting KVM_REQ_EVENT" operations listed in my comments above, do you mean we still need to keep the costly code above inside "if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win) {}" in function vcpu_enter_guest() as it used to be? If yes, my question is what is the exact purpose of "checking ON and setting KVM_REQ_EVENT" operations? Here is the code flow in vcpu_enter_guest(): 1. Check KVM_REQ_EVENT, if it is set, sync pir->virr 2. Disable interrupts 3. Check ON and set KVM_REQ_EVENT -- Here, we set KVM_REQ_EVENT, but it is checked in the step 1, which means, we cannot get any benefits even we set it here, since the "pir->virr" sync operation was done in step 1, between step 3 and VM-Entry, we don't synchronize the pir to virr. So even we set KVM_REQ_EVENT here, the interrupts remaining in PIR cannot be delivered to guest during this VM-Entry, right? Thanks, Feng > > > I might miss something in your comments, if so please point out. Thanks a > lot! > > > > Thanks, > > Feng > > > > > > > > > > > > > "if (kvm_x86_ops->hwapic_irr_update) > > > > kvm_x86_ops->hwapic_irr_update(vcpu, > > > > kvm_lapic_find_highest_irr(vcpu)); > > > > > > > > > kvm_lapic_find_highest_irr(vcpu) eats some cache > > > > > (4 cachelines) versus 1 cacheline for reading ON bit. > > > > > > > > > > > > > > Please remove blocked and wakeup_cpu, they should not be > > > necessary. > > > > > > > > > > > > > > > > Why do you think wakeup_cpu is not needed, when vCPU is > blocked, > > > > > > > > wakeup_cpu saves the cpu which the vCPU is blocked on, after > vCPU > > > > > > > > is woken up, it can run on a different cpu, so we need wakeup_cpu > to > > > > > > > > find the right list to wake up the vCPU. > > > > > > > > > > > > > > If the vCPU was moved it should have updated IRTE destination field > > > > > > > to the pCPU which it has moved to? > > > > > > > > > > > > Every time a vCPU is scheduled to a new pCPU, the IRTE destination > filed > > > > > > would be updated accordingly. > > > > > > > > > > > > When vCPU is blocked. To wake up the blocked vCPU, we need to find > > > which > > > > > > list the vCPU is blocked on, and this is what wakeup_cpu used for? > > > > > > > > > > Right, perhaps prev_vcpu is a better name. > > > > > > > > Do you mean "prev_pcpu"? > > > > > > Yes. > > > > > > > -- > > To unsubscribe from this list: send the line "unsubscribe kvm" in > > the body of a message to majordomo@xxxxxxxxxxxxxxx > > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
