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Date: Thu, 19 Apr 2018 23:44:05 +0300
From: Konstantin Belousov <kostikbel@gmail.com>
To: Colin Percival <cperciva@tarsnap.com>
Cc: freebsd-hackers@freebsd.org
Subject: Re: RFC: Hiding per-CPU kernel output behind bootverbose
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On Thu, Apr 19, 2018 at 06:06:21PM +0000, Colin Percival wrote:
> On large systems (e.g., EC2's x1e.32xlarge instance type, with 128 vCPUs)
> the boot time console output contains a large number of lines of the forms
> 
> SMP: AP CPU #N Launched!
> cpuN: <ACPI CPU> on acpi0
> estN: <Enhanced SpeedStep Frequency Control> on cpuN
> 
> Having 128 almost-identical lines of output doesn't seem very useful, and
> it actually has a nontrivial impact on the time spent booting.
> 
> Does anyone mind if I hide these by default, having them only show up if
> boot verbosity is requested?

The 'CPU XX Launched' messages are very useful for initial diagnostic
of the SMP startup failures. You need to enable bootverbose to see the
hang details, but for initial hint they are required. Unfortunately, AP
startup hangs occur too often to pretend that this can be delegated to
very specific circumstances.

Rest of the lines you pasted are normal device attach messages, so it is
not clear how would you hide them without ugly hacks.