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

From: Christian Borntraeger
Subject: Re: [Qemu-devel] [PATCH v8 1/1] crypto: add virtio-crypto driver
Date: Thu, 12 Jan 2017 15:10:25 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.6.0

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? 

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