Re: [patch] remove vcpu_info array v5

[Anthony Liguori <aliguori@us.ibm.com>]

Avi Kivity wrote:
>
>> My patch gets rid of the pointless MAX_CPUS sized array, which doesn't
>> buy us anything. In fact, most of the changes in my patch makes the
>> code simpler, because it removes a stack of silly cases where qemu uses
>> env->cpu_index to get into the array, just to hide CPUState from libkvm,
>> just to have the callback in QEMU go from int vcpu back to CPUState.
>>
>> Lets just do it right and get rid of this silliness.
>
> I agree that vcpu_info should die.  But we should still have a fast 
> way of getting a cpu from a cpu_index.  I don't see a problem with a 
> static array of pointers, make it 16K in size if you want.  Our real 
> scaling limits are much lower; they involve the big qemu lock and the 
> single iothread which will both limit scaling far below any static 
> vcpu array.

Just do a linear search of the CPUState list and be done with it.  This 
smells of premature optimization greatly.  I would be amazed if walking 
the CPUState list is ever on the fast path or will ever be.  Really, if 
you need to go from cpu_index => CPUState, it suggests you're doing 
something wrong.

Regards,

Anthony Liguori