Re: [PATCH 0/8] RFC: vcpu pinning at qemu start

[Glauber Costa <gcosta@redhat.com>]

Anthony Liguori wrote:
> Glauber Costa wrote:
>> Anthony Liguori wrote:
>>
>> No, it can't. Because at the time qemu starts, no vcpu -> thread id 
>> relationship exists at all. And we don't know when it will.
> 
> Sure we do.  The vcpu -> thread id relationship is valid after 
> kvm_init_ap() is called which is after machine init but before the 
> select loop is entered for the first time.  Therefore, if you start qemu 
> with -S, then connect on the monitor, and do an info cpus, you could be 
> guaranteed to be told the mapping.

I missed that. This changes everything. I now completely agree with you.

I'll post patches that expose the relationship, if it's better.

> The threads are *idle* at this point so there's no harm if they were 
> started on the "wrong" CPU.  You can now taskset to your hearts content 
> and then when you're happy with placement, you can issue a 'cont' so 
> that the VM actually starts running.  I saw "wrong" because you can 
> still taskset the initial creation guaranteeing that the threads are 
> created on the right group of physical CPUs, you just can't specify the 
> exact mapping until you start interacting with the monitor.
> 
> Regards,
> 
> Anthony Liguori
> 
>>> Regards,
>>>
>>> Anthony Liguori
>>>
>>>>
>>>>
>>>
>>
> 


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