Re: [PATCH v3] dm: switch dm-verity to async hash crypto API

On 02/19/2017 01:46 PM, Gilad Ben-Yossef wrote:

Use of the synchronous digest API limits dm-verity to using pure
CPU based algorithm providers and rules out the use of off CPU
algorithm providers which are normally asynchronous by nature,
potentially freeing CPU cycles.

This can reduce performance per Watt in situations such as during
boot time when a lot of concurrent file accesses are made to the
protected volume.

Move DM_VERITY to the asynchronous hash API.

Signed-off-by: Gilad Ben-Yossef <gilad@benyossef.com>
CC: Eric Biggers <redacted>
CC: Ondrej Mosnáček <redacted>
CC: Milan Broz <redacted>
---

The patch was tested on an Armv7 based dual core Zynq ZC706 development
board with SHA256-asm, SHA256-neon synchronous providers with no visible
degradation of performance, with cryptd based asynchronous versions of the 
same and with an off tree Arm CryptoCell asynchronous provider.

Changes from v2:

- Use completion to potentially wait also on crypto_ahash_init() as it
  may finish asynchronously as well in some drivers, such as cryptd, as
  discovered by Milan Broz.

This version survived my simple veritysetup test (in cryptsetup package)
with forced async path so I think it is ok for 4.12 queue...

Thanks,
Milan

- Use sg_init_one() where apropriate as pointed out by Milan Broz.

Changes from v1:

- Use a 0 mask to allocate crypto alg indicating we welcome async algo 
  providers, as suggested by Ondrej Mosnáček.
- Fix use of un-initialized completion when using async provider for IO
  blocks hashing
- Pass flag indicating we are OK with crypto provider backlog
- Re-factor checking for need to wait into a common function