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Date: Wed, 30 Jan 2019 17:41:37 +0100
From: Michael Mueller <mimu@...ux.ibm.com>
To: pmorel@...ux.ibm.com, Halil Pasic <pasic@...ux.ibm.com>
Cc: KVM Mailing List <kvm@...r.kernel.org>,
Linux-S390 Mailing List <linux-s390@...r.kernel.org>,
linux-kernel@...r.kernel.org,
Martin Schwidefsky <schwidefsky@...ibm.com>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Christian Borntraeger <borntraeger@...ibm.com>,
Janosch Frank <frankja@...ux.ibm.com>,
David Hildenbrand <david@...hat.com>,
Cornelia Huck <cohuck@...hat.com>
Subject: Re: [PATCH v6 12/13] KVM: s390: add gib_alert_irq_handler()
On 30.01.19 17:24, Pierre Morel wrote:
> On 29/01/2019 16:29, Michael Mueller wrote:
>>
>>
>> On 29.01.19 14:26, Halil Pasic wrote:
>>> On Thu, 24 Jan 2019 13:59:38 +0100
>>> Michael Mueller <mimu@...ux.ibm.com> wrote:
>>>
>>>> The patch implements a handler for GIB alert interruptions
>>>> on the host. Its task is to alert guests that interrupts are
>>>> pending for them.
>>>>
>>>> A GIB alert interrupt statistic counter is added as well:
>>>>
>>>> $ cat /proc/interrupts
>>>> CPU0 CPU1
>>>> ...
>>>> GAL: 23 37 [I/O] GIB Alert
>>>> ...
>>>>
>>>> Signed-off-by: Michael Mueller <mimu@...ux.ibm.com>
>>> [..]
>>>> +/**
>>>> + * gisa_get_ipm_or_restore_iam - return IPM or restore GISA IAM
>>>> + *
>>>> + * @gi: gisa interrupt struct to work on
>>>> + *
>>>> + * Atomically restores the interruption alert mask if none of the
>>>> + * relevant ISCs are pending and return the IPM.
>>>
>>> The word 'relevant' probably reflects some previous state. It does not
>>> bother me too much.
>>
>> "relevant" refers to the ISCs handled by the GAL mechanism, i.e those
>> registered in the kvm->arch.gisa_int.alert.mask.
>>
>>>
>>> [..]
>>>
>>>> +static void __airqs_kick_single_vcpu(struct kvm *kvm, u8
>>>> deliverable_mask)
>>>> +{
>>>> + int vcpu_id, online_vcpus = atomic_read(&kvm->online_vcpus);
>>>> + struct kvm_s390_gisa_interrupt *gi = &kvm->arch.gisa_int;
>>>> + struct kvm_vcpu *vcpu;
>>>> +
>>>> + for_each_set_bit(vcpu_id, kvm->arch.idle_mask, online_vcpus) {
>>>> + vcpu = kvm_get_vcpu(kvm, vcpu_id);
>>>> + if (psw_ioint_disabled(vcpu))
>>>> + continue;
>>>> + deliverable_mask &= (u8)(vcpu->arch.sie_block->gcr[6] >> 24);
>>>> + if (deliverable_mask) {
>>>> + /* lately kicked but not yet running */
>>>
>>> How about /* was kicked but didn't run yet */?
>>
>> what is the difference here...
>>
>>>
>>>> + if (test_and_set_bit(vcpu_id, gi->kicked_mask))
>>>> + return;
>>>> + kvm_s390_vcpu_wakeup(vcpu);
>>>> + return;
>>>> + }
>>>> + }
>>>> +}
>>>> +
>>>
>>> [..]
>>>
>>>> +static void process_gib_alert_list(void)
>>>> +{
>>>> + struct kvm_s390_gisa_interrupt *gi;
>>>> + struct kvm_s390_gisa *gisa;
>>>> + struct kvm *kvm;
>>>> + u32 final, origin = 0UL;
>>>> +
>>>> + do {
>>>> + /*
>>>> + * If the NONE_GISA_ADDR is still stored in the alert list
>>>> + * origin, we will leave the outer loop. No further GISA has
>>>> + * been added to the alert list by millicode while processing
>>>> + * the current alert list.
>>>> + */
>>>> + final = (origin & NONE_GISA_ADDR);
>>>> + /*
>>>> + * Cut off the alert list and store the NONE_GISA_ADDR in the
>>>> + * alert list origin to avoid further GAL interruptions.
>>>> + * A new alert list can be build up by millicode in parallel
>>>> + * for guests not in the yet cut-off alert list. When in the
>>>> + * final loop, store the NULL_GISA_ADDR instead. This will re-
>>>> + * enable GAL interruptions on the host again.
>>>> + */
>>>> + origin = xchg(&gib->alert_list_origin,
>>>> + (!final) ? NONE_GISA_ADDR : NULL_GISA_ADDR);
>>>> + /*
>>>> + * Loop through the just cut-off alert list and start the
>>>> + * gisa timers to kick idle vcpus to consume the pending
>>>> + * interruptions asap.
>>>> + */
>>>> + while (origin & GISA_ADDR_MASK) {
>>>> + gisa = (struct kvm_s390_gisa *)(u64)origin;
>>>> + origin = gisa->next_alert;
>>>> + gisa->next_alert = (u32)(u64)gisa;
>>>> + kvm = container_of(gisa, struct sie_page2, gisa)->kvm;
>>>> + gi = &kvm->arch.gisa_int;
>>>> + if (hrtimer_active(&gi->timer))
>>>> + hrtimer_cancel(&gi->timer);
>>>> + hrtimer_start(&gi->timer, 0, HRTIMER_MODE_REL);
>>>> + }
>>>> + } while (!final);
>>>> +
>>>> +}
>>>> +
>>>> void kvm_s390_gisa_clear(struct kvm *kvm)
>>>> {
>>>> struct kvm_s390_gisa_interrupt *gi = &kvm->arch.gisa_int;
>>>> if (!gi->origin)
>>>> return;
>>>> - memset(gi->origin, 0, sizeof(struct kvm_s390_gisa));
>>>> - gi->origin->next_alert = (u32)(u64)gi->origin;
>>>> + gisa_clear_ipm(gi->origin);
>>>
>>> This could be a separate patch. I would like little more explanation
>>> to this.
>>
>> I can break at out as I had before... ;)
>>
>>>
>>>> VM_EVENT(kvm, 3, "gisa 0x%pK cleared", gi->origin);
>>>> }
>>>> @@ -2940,13 +3078,25 @@ void kvm_s390_gisa_init(struct kvm *kvm)
>>>> gi->origin = &kvm->arch.sie_page2->gisa;
>>>> gi->alert.mask = 0;
>>>> spin_lock_init(&gi->alert.ref_lock);
>>>> - kvm_s390_gisa_clear(kvm);
>>>> + gi->expires = 50 * 1000; /* 50 usec */
>>>
>>> I blindly trust your choice here ;)
>>
>> You know I will increase it to 1 ms together with the change that I
>> proposed. (gisa_get_ipm_or_restore_iam() in kvm_s390_handle_wait()).
>
> With this.
> Reviewed-by: Pierre Morel<pmorel@...ux.ibm.com>
Pierre,
please see my mail with the measurements that I have done. Up to that
I can't take your Reviewed-by. I will keep the 50 usec.
Michael
>
>
>
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