linux-kernel - Re: [GIT PULL] Device tree updates for v3.12

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Date:	Wed, 11 Sep 2013 10:02:40 -0700
From:	Tony Luck <tony.luck@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Tim Bird <tbird20d@...il.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [GIT PULL] Device tree updates for v3.12

On Tue, Sep 10, 2013 at 1:50 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> Of course, maybe even the stupid add_device_randomness() is fast
> enough. I just wanted to point out that it definitely isn't some
> optimized thing.

When I posted the patch that mixes in the whole SMBIOS table:

commit d114a33387472555188f142ed8e98acdb8181c6d
Author: Tony Luck <tony.luck@...el.com>
Date:   Fri Jul 20 13:15:20 2012 -0700

    dmi: Feed DMI table to /dev/random driver

I asked whether there was any size issue - as it tends to be a few
kilobytes on laptops and desktops, and tens of kilobytes on servers.
The answer I got back then was not to worry - digesting a few kilobytes
wouldn't be a problem.  I just threw in a debug message to check and saw:

dmi_walk_early: added 10342 bytes in 339968 cycles

So a couple of hundred microseconds for me.

There are plenty of machine specific values buried in there (e.g. serial
numbers for all the DIMMs) ... so this looks like a good use of this
much boot time.

-Tony
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