linux-kernel - Re: [PATCH v5 13/15] KVM: s390: add function process_gib_alert

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Date:   Wed, 9 Jan 2019 13:14:17 +0100
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     mimu@...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 v5 13/15] KVM: s390: add function process_gib_alert_list()

On 08/01/2019 16:21, Michael Mueller wrote:
> 
> 
> On 08.01.19 13:59, Halil Pasic wrote:
>> On Wed, 19 Dec 2018 20:17:54 +0100
>> Michael Mueller <mimu@...ux.ibm.com> wrote:
>>
>>> This function processes the Gib Alert List (GAL). It is required
>>> to run when either a gib alert interruption has been received or
>>> a gisa that is in the alert list is cleared or dropped.
>>>
>>> The GAL is build up by millicode, when the respective ISC bit is
>>> set in the Interruption Alert Mask (IAM) and an interruption of
>>> that class is observed.
>>>
>>> Signed-off-by: Michael Mueller <mimu@...ux.ibm.com>
>>> ---
>>>   arch/s390/kvm/interrupt.c | 140 
>>> ++++++++++++++++++++++++++++++++++++++++++++++
>>>   1 file changed, 140 insertions(+)
>>>
>>> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
>>> index 48a93f5e5333..03e7ba4f215a 100644
>>> --- a/arch/s390/kvm/interrupt.c
>>> +++ b/arch/s390/kvm/interrupt.c
>>> @@ -2941,6 +2941,146 @@ int kvm_s390_get_irq_state(struct kvm_vcpu 
>>> *vcpu, __u8 __user *buf, int len)
>>>       return n;
>>>   }
>>> +static int __try_airqs_kick(struct kvm *kvm, u8 ipm)
>>> +{
>>> +    struct kvm_s390_float_interrupt *fi = &kvm->arch.float_int;
>>> +    struct kvm_vcpu *vcpu = NULL, *kick_vcpu[MAX_ISC + 1];
>>> +    int online_vcpus = atomic_read(&kvm->online_vcpus);
>>> +    u8 ioint_mask, isc_mask, kick_mask = 0x00;
>>> +    int vcpu_id, kicked = 0;
>>> +
>>> +    /* Loop over vcpus in WAIT state. */
>>> +    for (vcpu_id = find_first_bit(fi->idle_mask, online_vcpus);
>>> +         /* Until all pending ISCs have a vcpu open for airqs. */
>>> +         (~kick_mask & ipm) && vcpu_id < online_vcpus;
>>> +         vcpu_id = find_next_bit(fi->idle_mask, online_vcpus, 
>>> vcpu_id)) {
>>> +        vcpu = kvm_get_vcpu(kvm, vcpu_id);
>>> +        if (psw_ioint_disabled(vcpu))
>>> +            continue;
>>> +        ioint_mask = (u8)(vcpu->arch.sie_block->gcr[6] >> 24);
>>> +        for (isc_mask = 0x80; isc_mask; isc_mask >>= 1) {
>>> +            /* ISC pending in IPM ? */
>>> +            if (!(ipm & isc_mask))
>>> +                continue;
>>> +            /* vcpu for this ISC already found ? */
>>> +            if (kick_mask & isc_mask)
>>> +                continue;
>>> +            /* vcpu open for airq of this ISC ? */
>>> +            if (!(ioint_mask & isc_mask))
>>> +                continue;
>>> +            /* use this vcpu (for all ISCs in ioint_mask) */
>>> +            kick_mask |= ioint_mask;
>>> +            kick_vcpu[kicked++] = vcpu;
>>
>> Assuming that the vcpu can/will take all ISCs it's currently open for
>> does not seem right. We kind of rely on this assumption here, or?

why does it not seem right?

> 
> My latest version of this routine already follows a different strategy.
> It looks for a horizontal distribution of pending ISCs among idle vcpus.
> 

May be you should separate the GAL IRQ handling and the algorithm of the 
vCPU to kick in different patches to ease the review.


Regards,
Pierre

-- 
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany