linux-kernel - Re: [RFC PATCH 0/14] Parallel memory initialisation

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Message-ID: <20150415144818.GX5029@twins.programming.kicks-ass.net>
Date:	Wed, 15 Apr 2015 16:48:18 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Waiman Long <waiman.long@...com>, Linux-MM <linux-mm@...ck.org>,
	Nathan Zimmer <nzimmer@....com>, Daniel Rahn <drahn@...e.com>,
	Davidlohr Bueso <dbueso@...e.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Tom Vaden <tom.vaden@...com>,
	Scott Norton <scott.norton@...com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/14] Parallel memory initialisation

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.
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