Re: [Qemu-devel] [PATCH v8 1/1] crypto: add virtio-crypto driver

[Christian Borntraeger]

On 01/10/2017 01:56 PM, Christian Borntraeger wrote:
> On 01/10/2017 01:36 PM, Gonglei (Arei) wrote:
>> Hi,
>>
>>>
>>> On 12/15/2016 03:03 AM, Gonglei wrote:
>>> [...]
>>>> +
>>>> +static struct crypto_alg virtio_crypto_algs[] = { {
>>>> +  .cra_name = "cbc(aes)",
>>>> +  .cra_driver_name = "virtio_crypto_aes_cbc",
>>>> +  .cra_priority = 501,
>>>
>>>
>>> This is still higher than the hardware-accelerators (like intel aesni or the
>>> s390 cpacf functions or the arm hw). aesni and s390/cpacf are supported by 
>>> the
>>> hardware virtualization and available to the guests. I do not see a way how
>>> virtio
>>> crypto can be faster than that (in the end it might be cpacf/aesni + 
>>> overhead)
>>> instead it will very likely be slower.
>>> So we should use a number that is higher than software implementations but
>>> lower than the hw ones.
>>>
>>> Just grepping around, the software ones seem be be around 100 and the
>>> hardware
>>> ones around 200-400. So why was 150 not enough?
>>>
>> I didn't find a documentation about how we use the priority, and I assumed
>> people use virtio-crypto will configure hardware accelerators in the
>> host. So I choosed the number which bigger than aesni's priority.
> 
> Yes, but the aesni driver will only bind if there is HW support in the guest.
> And if aesni is available in the guest (or the s390 aes function from cpacf)
> it will always be faster than the same in the host via virtio.So your priority
> should be smaller.


any opinion on this?