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SubjectRe: [kvm-devel] [PATCH][RFC] kvm-scheduler integration
Rusty Russell wrote:
> On Sun, 2007-07-08 at 15:48 +0200, Ingo Molnar wrote:
>
>> * Avi Kivity <avi@qumranet.com> wrote:
>>
>>
>>>>> +#ifdef CONFIG_SCHED_KVM
>>>>> +static __read_mostly struct sched_kvm_hooks kvm_hooks;
>>>>> +#endif
>>>>>
>>>> please just add a current->put_vcpu() function pointer instead of
>>>> this hooks thing.
>>>>
>>> Won't that increase task_struct (16 bytes on 64-bit) unnecessarily?
>>> The function pointers are common to all virtual machines.
>>>
>> well, this function pointer could then be reused by other virtual
>> machines as well, couldnt it? If the task struct overhead is a problem
>> (it really isnt, and it's dependent on CONFIG_KVM) then we could switch
>> it around to a notifier-alike mechanism.
>>
>
> OK, this patch is *ugly*. Not that there's anything wrong with a patch
> which says "I'm going to preempt you", but making it kvm-specific is
> ugly. ISTR times past where I wanted such a hook, although none spring
> immediately into my pre-coffee brain.
>
> I think a "struct preempt_ops *" and a "void *preempt_ops_data" inside
> every task struct is a better idea. Call the config option
> PREEMPT_SCHED_HOOKS and now there's nothing kvm-specific about it...
>

I considered that, but your proposal does not allow a single task to
have multiple preemption hooks installed (hookers?!). Since in general
there's no reason to suppose that users would be mutually exclusive, we
need to have a struct hlist of these things. All in all this seemed to
indicate that the second user should have the honor of figuring out that
stuff.

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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