Re: [PATCH] fscrypt: don't use hardware offload Crypto API drivers

Maxime MERE
2025-06-25T18:30:01Z

Hi,

On 6/25/25 08:32, Eric Biggers wrote:
> That was the synchronous throughput. However, submitting multiple requests
> asynchronously (which again, fscrypt doesn't actually do) barely helps.
> Apparently the STM32 crypto engine has only one hardware queue.
>
> I already strongly suspected that these non-inline crypto engines aren't worth
> using. But I didn't realize they are quite this bad. Even with AES on a
> Cortex-A7 CPU that lacks AES instructions, the CPU is much faster!

From a performance perspective, using hardware crypto offloads the CPU,
which is important in real-world applications where the CPU must handle
multiple tasks. Our processors are often single-core and not the highest
performing, so hardware acceleration is valuable.

I can show you performance test realized with openSSL (3.2.4) who shows,
less CPU usage and better performance for large block of data when our
driver is used (via afalg):

command used: ```openssl speed -evp aes-256-cbc -engine afalg -elapsed```

+--------------------+--------------+-----------------+
| Block Size (bytes) | AFALG (MB/s) | SW BASED (MB/s) |
+--------------------+--------------+-----------------+
| 16 | 0.09 | 9.44 |
| 64 | 0.34 | 11.43 |
| 256 | 1.31 | 12.08 |
| 1024 | 4.96 | 12.27 |
| 8192 | 18.18 | 12.33 |
| 16384 | 22.48 | 12.33 |
+--------------------+--------------+-----------------+

to test CPU usage I've used a monocore stm32mp157f.
here with afalg, we have an average CPU usage of ~75%, with the sw based
approach CPU is used at ~100%

Maxime