Re: What happens before or in `schedule_preempt_disabled()`?

From: Paul Menzel
Date: Wed Oct 17 2018 - 12:47:14 EST

Dear Thomas,

As always thank you for the quick reply.

On 10/17/18 18:39, Thomas Gleixner wrote:

> On Wed, 17 Oct 2018, Paul Menzel wrote:
>> Please find the debug patches attached. The `random: %i` messages are from
>> `crng_fast_load()`.
>> My question is, how can I figure out, what happens in the code below?
>> complete(&kthreadd_done);
>> pr_info("After kthreadd_done\n");
>> /*
>> * The boot idle thread must execute schedule()
>> * at least once to get things moving:
>> */
>> schedule_preempt_disabled();
>> pr_info("After schedule_preempt_disabled\n");
>> Looking at `schedule_preempt_disabled()`, it shouldnʼt take much time, and I
>> was unable to find out where `crng_fast_load()` is called from.
>> I guess threading is somehow working at that point, and I would though that
>> it is the `complete()` call, but wonder why the `After kthreadd_done` is
>> printed earlier.
> This creates the init thread from the idle thread with preemption
> disabled. To get the init thread on the CPU the idle thread must schedule
> voluntary, which it does by calling schedule_preempt_disabled(). So the
> scheduler picks the init thread and that executes the init callbacks.
> The random calls are invoked by add_interrupt_randomness() or
> add_hwgenerator_randomness(). But they are probably not consuming all the
> time.
> The time is consumed by the initcalls which are required before bringing up
> the (non boot) CPUs. See kernel_init_freeable() which is called from
> kernel_init(). If you add initcall_debug to the command line you will get
> more information at least about the functions which are marked with
> initcall.

Thank you for the quick reply. Just a note, that `initcall_debug` is present
on the Linux kernel command line. (I didnʼt mention that the full output of
`dmesg` was attached to my message.

[ 0.078186] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-4.19.0-rc8-00045-gc92161e11c2a root=/dev/sda1 rw noisapnp cryptomgr.notests quiet initcall_debug init=/lib/systemd/systemd-bootchart iomem=relaxed apparmor=0 selinux=0 kmemleak=off initcall_blacklist=serial8250_init,init_graph_trace udev.children_max=2 udev.log_priority=info

Thank you again for the pointers. Iʼll look into those.

Kind regards,


Attachment: smime.p7s
Description: S/MIME Cryptographic Signature