linux-kernel - Re: [PATCH v8 1/1] crypto: add virtio-crypto driver

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Date:   Thu, 12 Jan 2017 15:10:25 +0100
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     "Gonglei (Arei)" <arei.gonglei@...wei.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
        "virtio-dev@...ts.oasis-open.org" <virtio-dev@...ts.oasis-open.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>
Cc:     "Huangweidong (C)" <weidong.huang@...wei.com>,
        Claudio Fontana <Claudio.Fontana@...wei.com>,
        "mst@...hat.com" <mst@...hat.com>,
        Luonengjun <luonengjun@...wei.com>,
        "Hanweidong (Randy)" <hanweidong@...wei.com>,
        "Xuquan (Quan Xu)" <xuquan8@...wei.com>,
        "Wanzongshun (Vincent)" <wanzongshun@...wei.com>,
        "stefanha@...hat.com" <stefanha@...hat.com>,
        "Zhoujian (jay, Euler)" <jianjay.zhou@...wei.com>,
        longpeng <longpeng2@...wei.com>,
        "arei.gonglei@...mail.com" <arei.gonglei@...mail.com>,
        "Wubin (H)" <wu.wubin@...wei.com>
Subject: Re: [PATCH v8 1/1] crypto: add virtio-crypto driver

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?