linux-kernel - Re: [PATCH] init/main.c: Use ktime accessor function in initcall

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Date:	Thu, 20 Nov 2008 10:28:07 -0800
From:	Tim Bird <tim.bird@...sony.com>
To:	Will Newton <will.newton@...il.com>
CC:	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] init/main.c: Use ktime accessor function in initcall_debug
 code.

Will Newton wrote:
> On Thu, Nov 20, 2008 at 5:39 PM, Tim Bird <tim.bird@...sony.com> wrote:
>> Will Newton wrote:
>>> The initcall_debug code access the tv64 member of ktime. This won't work
>>> correctly for large deltas on platforms that don't use the scalar ktime
>>> implementation.
>> In principle I see no problem with this.  But as a matter of
>> practice it may be overkill.
> 
> Possibly, but it makes the code clearer I think.
> 
>> How big does the delta have to be for this to be a problem?
>> And how much overhead does ktime_to_ns() add?
> 
> Deltas over a second will be incorrect.

OK.  Good fix, then.

> I have serial8250_init taking
> 8 seconds at the moment, so that isn't unheard of.

This is likely the result of the emission of all
previously queued printks which occurs during serial8250_init()
(as a side effect of finally initializing the console).

I see this kind of long delay all the time.
If the 8 seconds is a bother, you might want
to use 'quiet' on the kernel command line.

I suspect you've already seen this page, but for future
readers of this thread, there's info on this at:
http://elinux.org/Disable_Console

> On scalar ktime architectures it should be zero, on others a multiply
> and an add (it's an inline). I wouldn't call it a fast path though.

OK.  You have my ACK.
 -- Tim

=============================
Tim Bird
Architecture Group Chair, CE Linux Forum
Senior Staff Engineer, Sony Corporation of America
=============================

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