Re: [PATCH] crypto: allow to assign gfp_t for __crypto_alloc_tfm

[Steffen Klassert <steffen.klassert@secunet.com>]

On Tue, May 19, 2015 at 10:27:55PM +0800, Herbert Xu wrote:
> On Tue, May 19, 2015 at 10:14:30AM -0400, Theodore Ts'o wrote:
> > 
> > There can be multiple reads going on in parallel, so we're currently
> > creating tfm's as necessary.  In fact one of the things that we've
> 
> A single tfm is fully-reentrant (as long as you don't change the
> key).  So multiple reads/writes on a single file can all use one
> tfm with no locking at all.
> 
> There should be a single tfm per key.  As your code appears to use
> one key per inode, that translates to one tfm per inode.
> 
> > talked about doing is since there are some ARM cores where their
> > "hardware acceleration" is slower than optimized software (sigh), and
> > there are some Android applications (such as Facebook) that read
> > *vast* quantities of data from flash on startup before painting a
> > single pixel, that we might want to consider in some cases,
> > parallelizing the decryption across multiple ARM cores.  Figuring out
> > when to do this, both in terms of the workload, how many cores to use
> > to balance off against power utilization, how much (if ever) to use
> > the hardware "accelerator", and just plain lack of time caused us not
> > to go down that particular path.
> 
> We already have some support for such parallelisation in the form of
> pcrypt.  It has been used on IPsec and I believe dmcrypt.

The current pcrypt version is used just for IPsec because it supports
only AEAD type algorithms and does not support request backlog. But
I have patches to support ablkcipher algorithms and request backlog.
I could provide them if there is interest in it.