Re: [dm-devel] [PATCH] DM-CRYPT: Scale to multiple CPUs

[Herbert Xu]

On Wed, Jun 02, 2010 at 01:10:00AM -0400, Mikulas Patocka wrote:
>
> And how can I use pcrypt for dm-crypt? After a quick look at pcrypt 
> sources, it seems to be dependent on aead and not useable for general 
> encryption algorithms at all.

You instantiate a pcrypt variant of whatever algorithm that you're
using.  For example, if you're using XTS then you should instantiate
pcrypt(xts(aes)).  Currently you must use tcrypt to instantiate.

> I tried cryptd --- in theory it should work by requesting the algorithm 
> like cryptd(cbc(aes)) --- but if I replace "%s(%s)" with "cryptd(%s(%s))" 
> in dm-crypt sources it locks up and doesn't work.

cryptd is something else altogether.  However, it certainly should
not lock up.  What kernel version is this?

> > This would be inappropriate for upper layer code as they do not
> > know whether the underlying algorithm should be parallelised,
> > e.g., a PCI offload board certainly should not be parallelised.
> 
> The upper layer should ideally request "cbc(aes)" and the crypto routine 
> should select the most efficient implementation --- sync on single-core 
> system, async with cryptd on multi-core system and async with hardware 
> implementation if you have HIFN crypto card.

That's exactly what will happen when the admin instantiates pcrypt.
dm-crypt simply needs to specify cbc(aes) and it will get pcrypt
automatically.

The point is that on a modern processor like Nehalem you don't need
pcrypt.
 
> It is pointless to track the submitting CPU.

No you are wrong.

Cheers,
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