Re: [PATCH v2 0/4] Introduce bulk mode for crypto engine framework

[Milan Broz]

On 04/18/2016 03:36 PM, Mike Snitzer wrote:
> On Mon, Apr 18 2016 at  1:31am -0400,
> Baolin Wang <baolin.wang@xxxxxxxxxx> wrote:
> 
>> Hi Herbert,
>>
>> On 15 April 2016 at 21:48, Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> wrote:
>>> On Tue, Mar 15, 2016 at 03:47:58PM +0800, Baolin Wang wrote:
>>>> Now some cipher hardware engines prefer to handle bulk block by merging requests
>>>> to increase the block size and thus increase the hardware engine processing speed.
>>>>
>>>> This patchset introduces request bulk mode to help the crypto hardware drivers
>>>> improve in efficiency.
>>>
>>> Could you please explain why this merging can't be done in dm-crypt
>>> instead?
>>
>> We've tried to do this in dm-crypt, but it failed.
>> The dm-crypt maintainer explained to me that I should optimize the
>> driver, not add strange hw-dependent crypto modes to dm-crypt, this is
>> not the first crypto accelerator that is just not suited for this kind
>> of use.
> 
> As a DM mainatiner my only contribution to this line of discussion was
> relative to your proposal to train the dm-crypt target (which is
> bio-based) to also provide request-based support, see:
> https://www.redhat.com/archives/dm-devel/2015-November/msg00112.html
> 
> But follow-up discussion occured, primarily with Milan Broz, which led
> to this bulk mode support in the crypto layer.  Pretty strange Milan
> wasn't cc'd on your patchset posting (I've now cc'd him).

My complaint was mainly that the proposed dmcrypt based version just did
not work properly.
https://lkml.org/lkml/2016/1/2/109

(I did not test the new version we are replying here. I wonder how the problem
I mentioned is fixed though.
Also see Mikulas' comments https://www.redhat.com/archives/dm-devel/2016-January/msg00145.html)
 
Anyway, all this seems to optimize case for specific crypto hw, that
is not able to perform optimally with pattern dmcrypt produces.

I do not think dmcrypt should do optimizations for specific hw.

But if we decide that it is needed there, it should not cause any performance
or compatibility problems elsewhere...

Milan