Re: Hardware acceleration indication in af_alg

[Matthias-Christian Ott <ott@mirix.org>]

On Fri, Oct 21, 2011 at 04:15:41PM +0200, Matthias-Christian Ott wrote:
> On Fri, Oct 21, 2011 at 03:23:36PM +0200, Herbert Xu wrote:
> > Matthias-Christian Ott <ott@mirix.org> wrote:
> > > I did some experiments with af_alg and noticed that to be really
> > > useful, it should indicate whether a certain algorithm is hardware
> > > accelerated. I guess this has to be inferred by the priority of the
> > > algorithm could be made available via a read-only socket option. Any
> > > thoughts on this?
> > > 
> > > I can imagine, an alternative approach and perhaps better approach
> > > would be to measure the speed of the kernel provided algorithm against
> > > a software implementation, but there are many other factors that could
> > > influence the results. Therefore, it is perhaps better to just make
> > > the assumption that hardware acceleration is faster which is made in
> > > the kernel anyhow.
> > 
> > You have to be careful to distinguish between hardware acceleration
> > that is directly available to user-space (such as AESNI) and those
> > that aren't.
> > 
> > For the former it makes zero sense to go through the kernel as
> > you'll only make it slower.  The latter case is the reason why
> > this interface exists.
> 
> This is why I didn't consider hardware acceleration that is directly
> available to user-space in the first place (I'm not aware of anything
> except CPUs that is usable this way). So the question remains whether
> e.g. the AES implementation provided through af_alg by the kernel is
> faster (and thus most likely hardware accelerated) than a software
> implementation. Since the kernel seems to make the assumption that
> hardware acceleration is faster, I asked whether it would be possible to
> pass this information to user-space as well.

Ignore that e-mail. The the recent user configuration patches
by Stefan Klassert seem to expose the algorithm's priority via
CRYPTOCFGA_PRIORITY_VAL. This should solve my problem, provided that
the patches will be included.

Regards,
Matthias-Christian