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

[Eric Biggers <ebiggers@kernel.org>]

On Wed, Nov 09, 2022 at 06:37:38PM -0800, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
> 
> 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.
> 
> While this patch is an optimization and not a "fix" per se, I've marked
> it as for stable, due to the large improvement it can make to boot time.
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: Eric Biggers <ebiggers@google.com>

Unfortunately, this patch won't work because it breaks templates.

There should still be a solution that at least avoids having to spawn kthreads,
though...

- Eric