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

[Mikulas Patocka]

On Wed, 2 Jun 2010, Herbert Xu wrote:

> 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 "pcrypt(%s(%s))" in dm-crypt and I get "table: 253:0: crypt: Error 
allocating crypto tfm"

Are you sure that you know what you're talking about? pcrypt_alloc 
contains this:
switch (algt->type & algt->mask & CRYPTO_ALG_TYPE_MASK) {
case CRYPTO_ALG_TYPE_AEAD:
        return pcrypt_alloc_aead(tb);
}

return ERR_PTR(-EINVAL);
--- so for anything other byt AEAD it returns -EINVAL.

> > 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?

2.6.34 and cryptsetup 1.1.2. It is a soft lockup interruptible with 
Ctrl-C.

> > > 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.

For what? For avoiding cache bounces? But the encrypting is 
order-of-magnitude slower than memory speed.

Mikulas
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