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

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Message-ID: <f174540e-4b9a-4dc1-9ab8-f4f36fe1f837@foss.st.com>
Date: Wed, 25 Jun 2025 18:29:26 +0200
From: Maxime MERE <maxime.mere@...s.st.com>
To: Eric Biggers <ebiggers@...nel.org>,
        Simon Richter
	<Simon.Richter@...yros.de>
CC: <linux-fscrypt@...r.kernel.org>, <linux-crypto@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-mtd@...ts.infradead.org>,
        <linux-ext4@...r.kernel.org>, <linux-f2fs-devel@...ts.sourceforge.net>,
        <ceph-devel@...r.kernel.org>
Subject: Re: [PATCH] fscrypt: don't use hardware offload Crypto API drivers

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