-----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@MW5PR84M...
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.