linux-kernel - Re: [PATCH 0/5] crypto: add IV generation templates

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Date:   Thu, 19 Jul 2018 18:55:10 +0800
From:   Xiongfeng Wang <wangxiongfeng2@...wei.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Arnd Bergmann <arnd@...db.de>
CC:     Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        <dm-devel@...hat.com>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>,
        Jonathan Cameron <jonathan.cameron@...wei.com>
Subject: Re: [PATCH 0/5] crypto: add IV generation templates

Hi,

On 2018/7/18 23:34, Ard Biesheuvel wrote:
> On 18 July 2018 at 19:59, Arnd Bergmann <arnd@...db.de> wrote:
>> On Wed, Jul 18, 2018 at 9:30 AM, Xiongfeng Wang
>> <wangxiongfeng2@...wei.com> wrote:
>>>
>>> I tested the performance of software implemented ciphers before and after
>>> applying this patchset. The performance didn't change much except for
>>> slight regression when writting. The detail information is as follows.
>>>
>>> The command I used:
>>> cryptsetup -y -c aes-xts-plain -s 256 --hash sha256 luksFormat /dev/sdd1
>>> cryptsetup -y -c aes-cbc-essiv:sha256 -s 256 --hash sha256 luksFormat /dev/sdd1
>>> cryptsetup -y -c aes-cbc-benbi -s 256 --hash sha256 luksFormat /dev/sdd1
>>>
>>> cryptsetup luksOpen /dev/sdd1 crypt_fun
>>> time dd if=/dev/mapper/crypt_fun of=/dev/null bs=1M count=500 iflag=direct
>>> time dd if=/dev/zero of=/dev/mapper/crypt_fun bs=1M count=500 oflag=direct
>>>
>>> Performance comparision:
>>> --------------------------------------------------------
>>> algorithms      | before applying   |   after applying
>>> --------------------------------------------------------
>>>                 |  read  | write    |  read  | write
>>> --------------------------------------------------------
>>> aes-xts-plain   | 145.34 | 145.09   | 145.89 | 144.2
>>> --------------------------------------------------------
>>> aes-cbc-essiv   | 146.87 | 144.62   | 146.74 | 143.41
>>> --------------------------------------------------------
>>> aes-cbc-benbi   | 146.03 | 144.74   | 146.77 | 144.46
>>> --------------------------------------------------------
>>
>> Do you have any estimate of the expected gains for hardware
>> implementations?
>>
>> Would it make sense to try out implementing aes-cbc-essiv
>> on the ARMv8 crypto extensions? I see that Ard has done
>> some prior work on aes-ccm in arch/arm64/crypto/aes-ce-ccm-*
>> that (AFAICT) has a similar goal of avoiding overhead by
>> combining the usual operations, so maybe the same can
>> be done here.
>>
> 
> I am having trouble understanding what exactly this series aims to achieve.
> 
> Calling into the crypto layer fewer times is a nice goal, but a disk
> sector seems like a reasonable granularity for the dm layer to operate
> on, and I don't think any hardware exists that operates on multi
> sector sequences, where it would pay off to amortize the latency of
> invoking the hardware over an entire bio.

I don't know much about crypto hardware, but I think a crypto hardware can handle
data more than one sector at one time. So I think passing the whole bio to the hardware
at one time will decrease the overhead in passing each sector alternatively.

Thanks,
Xiongfeng
> 
> So in summary, you need to explain to us why we need this. It is
> really very easy to convince people if your changes make things go
> faster.
> 
> .
>