From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Paul Menzel <pmenzel+linux-serial@molgen.mpg.de>
Cc: linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: How to move serial8250_init out of the critical path to decrease boot time?
Date: Sun, 1 Apr 2018 10:05:46 +0200 [thread overview]
Message-ID: <20180401080546.GA31356@kroah.com> (raw)
In-Reply-To: <e086c888-df77-1fde-e3b8-9246c9ab3377@molgen.mpg.de>
On Sun, Apr 01, 2018 at 09:11:15AM +0200, Paul Menzel wrote:
> Dear Linux folks,
>
>
> The goal is to boot a *distribution* Linux kernel as fast as possible. (The
> goal is currently 500 ms.)
What distro?
> With Linux 4.16-rc7, `serial8250_init()` takes almost 34 ms according to
> `initcall_debug` on the laptop TUXEDO Book BU1406 with an Intel Kaby Lake
> processor.
>
> ```
> [ 2.657950] calling serial8250_init+0x0/0x168 @ 1
> [ 2.657963] Serial: 8250/16550 driver, 32 ports, IRQ sharing enabled
> [ 2.692598] initcall serial8250_init+0x0/0x168 returned 0 after 33820
> usecs
> ```
>
> One problem is, that the distributions do not build this as a module,
> despite more and more devices do not actually have serial connectors, but
> the chipset still exposes them.
Then fix that in the distro kernel build.
> What options are there?
File a bug with the distro.
> 1. Try to probe it asynchronously as in the attached patch, which is not
> tested yet.
Please test it and watch to see what breaks :)
good luck!
greg k-h
prev parent reply other threads:[~2018-04-01 8:05 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-01 7:11 How to move serial8250_init out of the critical path to decrease boot time? Paul Menzel
2018-04-01 8:05 ` Greg Kroah-Hartman [this message]
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