Re: irqdevice INTR example

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Gregory Haskins wrote:
> Out of curiosity, did you review my kick_process() version or the newer smp_call_function_single() based version of the patch?  
>
>   

The former.

>>     
>>> @@ -1866,6 +1874,19 @@ static int kvm_vcpu_ioctl_run(struct kvm_vcpu *vcpu, 
>>>       
>> struct kvm_run *kvm_run)
>>     
>>>  		kvm_arch_ops->decache_regs(vcpu);
>>>  	}
>>>  
>>> +	/*
>>> +	 * Make sure the current task is accurately recorded.  Most of the 
>>> +	 * time, it will be so we first check if its necessary without taking
>>> +	 * the lock.  If there is a mismatch, we must aquire the lock and 
>>> +	 * check again to eliminate races
>>> +	 */
>>> +	if (unlikely(vcpu->irq.task != current)) {
>>> +		spin_lock(&vcpu->irq.lock);
>>> +		if (vcpu->irq.task != current)
>>> +			vcpu->irq.task = current;
>>> +		spin_unlock(&vcpu->irq.lock);
>>> +	}
>>> +
>>>   
>>>       
>> Isn't this equivalent to
>>
>>     vcpu->irq.task = current
>>     
>
> Yeah, good point.  I originally had a printk in there to report when it changes, thus the conditional.  I didn't collapse it when I took the printk out.  I suppose you could argue that updating the variable indiscriminately will unnecessarily dirty a cache-line, but I doubt it would matter in the grand scheme of things.
>
>   

The vcpu cachelines are already dirty.

Please repost the patchset (one patch per message) so I can see it
together.  Thanks.

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


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