linux-kernel - Re: [RFC 0/2] Delay initializing of large sections of memory

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Date:	Fri, 21 Jun 2013 14:28:42 -0700
From:	Mike Travis <travis@....com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Nathan Zimmer <nzimmer@....com>, Robin Holt <holt@....com>,
	Rob Landley <rob@...dley.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	linux-doc@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 0/2] Delay initializing of large sections of memory



On 6/21/2013 12:00 PM, Yinghai Lu wrote:
> On Fri, Jun 21, 2013 at 11:44 AM, Greg Kroah-Hartman
> <gregkh@...uxfoundation.org> wrote:
>> On Fri, Jun 21, 2013 at 11:36:21AM -0700, Yinghai Lu wrote:
>>> On Fri, Jun 21, 2013 at 9:25 AM, Nathan Zimmer <nzimmer@....com> wrote:
>>>> This rfc patch set delays initializing large sections of memory until we have
>>>> started cpus.  This has the effect of reducing startup times on large memory
>>>> systems.  On 16TB it can take over an hour to boot and most of that time
>>>> is spent initializing memory.
>>>
>>> One hour on system with 16T ram? BIOS or OS?
>>>
>>> I use wall clock to check bootime on one system with 3T and 16 pcie cards,
>>> Linus only takes about 3m and 30 seconds from bootloader.
>>>
>>> wonder if you boot delay is with so many cpu get onlined in serialized mode.
>>>
>>> so can you try boot your system with "maxcpus=128" to get the boot time with
>>> wall clock ?
>>
>> Why use the "wall clock" when we have the wonderful bootchart tools and
>> scripts that do this all for you, and can tell you exactly what part of
>> the kernel is taking what time, to help with fixing issues like this?
> 
> bootchart is not completed.
> 
> printk timestamp come after mem get initialized.
> ....
> [    0.004000] tsc: Fast TSC calibration using PIT
> 
> before that stamp are all 0.
> 
> Yinghai
> 

On UV the system console function has an option to include
timestamps, both sequential in HH:MM:SS and deltas to 100ms.
So we get both the BIOS and system times before printk time
is active.  We also have a custom "script" command that adds
timing info.
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