Re: [PATCH v3 5/5] crypto: AES CBC multi-buffer glue code

[Tim Chen <tim.c.chen@linux.intel.com>]

On Thu, 2015-11-26 at 16:49 +0800, Herbert Xu wrote:
> On Tue, Nov 24, 2015 at 10:30:06AM -0800, Tim Chen wrote:
> >
> > On the decrypt path, we don't need to use multi-buffer algorithm
> > as aes-cbc decrypt can be parallelized inherently on a single
> > request.  So most of the time the outer layer algorithm
> > cbc_mb_async_ablk_decrypt can bypass mcryptd and
> > invoke mb_aes_cbc_decrypt synchronously
> > to do aes_cbc_dec when fpu is available.
> > This avoids the overhead of going through mcryptd.  Hence
> > the use of blkcipher on the inner layer.  For the mcryptd
> > path, we will complete a decrypt request in one shot so
> > blkcipher usage should be fine.
> 
> I think there is a misunderstanding here.  Just because you're
> using/exporting through the ablkcipher interface doesn't mean
> that you are asynchrounous.  For example, all blkcipher algorithms
> can be accessed through the ablkcipher interface and they of course
> remain synchrounous.
> 
> So I don't see how using an ablkcipher in the inner layer changes
> anything at all.  You can still return immediately and not bother
> with completion functions when you are synchrounous.
> 
> Cheers,

OK, I'll try to see if I can cast things back to the original ablkcipher
request and use that to walk the sg list.

Tim