RE: [PATCH] crypto: avoid unnecessary work when self-tests are disabled

["Elliott, Robert (Servers)" <elliott@hpe.com>]

> -----Original Message-----
> From: Eric Biggers <ebiggers@kernel.org>
> Sent: Wednesday, November 9, 2022 8:38 PM
> Subject: [PATCH] crypto: avoid unnecessary work when self-tests are
> disabled
> 
> Currently, registering an algorithm with the crypto API always causes a
> notification to be posted to the "cryptomgr", which then creates a
> kthread to self-test the algorithm.  However, if self-tests are disabled
> in the kconfig (as is the default option), then this kthread just
> notifies waiters that the algorithm has been tested, then exits.
> 
> This causes a significant amount of overhead, especially in the kthread
> creation and destruction, which is not necessary at all.  For example,
> in a quick test I found that booting a "minimum" x86_64 kernel with all
> the crypto options enabled (except for the self-tests) takes about 400ms
> until PID 1 can start.  Of that, a full 13ms is spent just doing this
> pointless dance, involving a kthread being created, run, and destroyed
> over 200 times.  That's over 3% of the entire kernel start time.
> 
> Fix this by just skipping the creation of the test larval and the
> posting of the registration notification entirely, when self-tests are
> disabled.  Also compile out the unnecessary code in algboss.c.
> 
...
> +#ifdef CONFIG_CRYPTO_MANAGER_DISABLE_TESTS
> +static int cryptomgr_schedule_test(struct crypto_alg *alg)
> +{
> +	return 0;
> +}
> +#else

The crypto/kdf_sp800108.c init function currently ignores both 
CONFIG_CRYPTO_MANAGER_DISABLE_TESTS and the cryptomgr module's
notests module parameter and always runs its self-test, as described in
https://lore.kernel.org/lkml/MW5PR84MB1842811C4EECC0F4B35B5FB3AB709@MW5PR84MB1842.NAMPRD84.PROD.OUTLOOK.COM/T/#t

Paul reported that taking 262 ms on his system; I measured 1.4 s on
my system.

It'd be nice if a patch series improving how DISABLE_TESTS is honored
would tackle that module too.