Re: jitterentropy: `jent_mod_init()` takes 17 ms

[Paul Menzel]

Dear Stephan,


Thank you for the quick reply.

Am 10.11.20 um 10:25 schrieb Stephan Mueller:
> Am Montag, 9. November 2020, 20:31:02 CET schrieb Paul Menzel:

> > 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
>
> Hm, 17.5 / 900 = 2%, or am I missing something?

Indeed, that is embarrassing. My bad.

> > 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.
>
> What you see is the test whether the Jitter RNG has a proper noise source. The
> function jent_entropy_init() is the cause of the operation. It performs 1024
> times a test to validate the appropriateness of the noise source. You can
> adjust that with the TESTLOOPCOUNT in this function. But I am not sure
> adjusting is a wise course of action.

Out of curiosity, why 1024 and not, for example, 128 or 2048? Is there 
some statistics behind it?


Kind regards,

Paul