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Date: Wed, 21 Nov 2012 16:08:58 +0100
From: Christian Borntraeger <borntraeger@de.ibm.com>
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Subject: Re: [Qemu-devel] [PATCH 1/3] s390/migration: Provide a cpu save for
 initial life migration work
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To: Alexander Graf <agraf@suse.de>
Cc: Jan Kiszka <jan.kiszka@siemens.com>, Jens Freimann <jfrei@linux.vnet.ibm.com>, Heinz Graalfs <graalfs@linux.vnet.ibm.com>, qemu-devel <qemu-devel@nongnu.org>, "Jason J. herne" <jjherne@us.ibm.com>

On 21/11/12 16:06, Alexander Graf wrote:
[...]
>>>>>> +static int cpu_post_load(void *opaque, int version_id)
>>>>>> +{
>>>>>> +    CPUS390XState *env = opaque;
>>>>>> +    struct kvm_fpu fpu;
>>>>>> +    int i, r;
>>>>>> +
>>>>>> +    if (!kvm_enabled()) {
>>>>>> +        return 0;
>>>>>> +    }
>>>>>> +
>>>>>> +    for (i = 0; i<    16; i++) {
>>>>>> +        fpu.fprs[i] = env->fregs[i].ll;
>>>>>> +    }
>>>>>> +    fpu.fpc = env->fpc;
>>>>>> +
>>>>>> +    r = kvm_vcpu_ioctl(env, KVM_SET_FPU,&fpu);
>>>>>> +    assert(r == 0);
>>>>>> +
>>>>>> +    return 0;
>>>>>> +}
>>>>> The kvm register sync needs to happen in the kvm register sync function :)
>>>> That would eliminate the whole purpose of sync regs and forces us to have an
>>>> expensive ioctl on lots of exits (again). I would prefer to sync the registers
>>>> that we never need in qemu just here.
>>> That's why the register sync has different stages.
>> Not the get_register. Which is called on every synchronize_state. Which happen quite often
>> on s390.
> 
> Sounds like bad design then :).
> 
> Maybe we should explicitly tell the register synchronization which register sets to sync, so that we don't waste time getting _all_ the state every time we sync registers?

Yes, a level statement for kvm_arch_get_registers would be good.