linux-kernel - jitterentropy: `jent_mod

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Date:   Mon, 9 Nov 2020 20:31:02 +0100
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Stephan Mueller <smueller@...onox.de>
Cc:     linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: jitterentropy: `jent_mod_init()` takes 17 ms

Dear Linux folks,

By mistake I built `XFRM_ESP` into the Linux kernel, resulting in

     CONFIG_CRYPTO_SEQIV=y
     CONFIG_CRYPTO_ECHAINIV=y

and also the Jitterentropy RNG to be built in.

     CRYPTO_JITTERENTROPY=y

So, on the Asus F2A85-M PRO starting Linux 4.10-rc3 with 
`initcall_debug`, the init method is run unconditionally, and it takes 
17.5 ms, which is over ten percent of the overall 900 ms the Linux 
kernel needs until loading the init process.

     [    0.300544] calling  jent_mod_init+0x0/0x2c @ 1
     [    0.318438] initcall jent_mod_init+0x0/0x2c returned 0 after 
17471 usecs

Looking at the output of systemd-bootchart, it looks like, that this 
indeed delayed the boot a little, as the other init methods seem to be 
ordered after it.

I am now building it as a module, but am wondering if the time can be 
reduced to below ten milliseconds.

Kind regards,

Paul