RE: [RFC PATCH 0/14] Parallel memory initialisation

[Norton, Scott J]

On 04/15/2015 10:48 AM, Peter Zijlstra wrote:
> On Wed, Apr 15, 2015 at 03:34:20PM +0100, Mel Gorman wrote:
>> On Wed, Apr 15, 2015 at 04:27:31PM +0200, Peter Zijlstra wrote:
>>> On Wed, Apr 15, 2015 at 09:15:50AM -0400, Waiman Long wrote:
>>>> I had included your patch with the 4.0 kernel and booted up a 
>>>> 16-socket 12-TB machine. I measured the elapsed time from the elilo 
>>>> prompt to the availability of ssh login. Without the patch, the 
>>>> bootup time was 404s. It was reduced to 298s with the patch. So 
>>>> there was about 100s reduction in bootup time (1/4 of the total).
>>> But you cheat! :-)
>>>
>>> How long between power on and the elilo prompt? Do the 100 seconds 
>>> matter on that time scale?
>>>
>> Calling it cheating is a *bit* harsh as the POST times vary 
>> considerably between manufacturers. While I'm interested in Waiman's 
>> answer, I'm told that those that really care about minimising reboot 
>> times will use kexec to avoid POST.  The 100 seconds is 100 seconds, 
>> whether that is 25% in all cases is a different matter.
>>
> Sure POST times vary, but its consistently stupid long :-) I'm forever 
> thinking my EX machine died because its not coming back from a power 
> cycle, and mine isn't really _that_ large.

Yes, 100 seconds really does matter and is a big deal. When a business has one of 
these large machines go down their business is stopped (unless they have a
fast failover solution in place). Every minute and second the machine is down 
is crucial to these businesses.  The fact that POST times can be so long make it
even more important that we make the kernel boot as fast as possible.

Scott

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