linux-kernel - Re: [PATCH,RFC] random: collect cpu randomness

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Date:	Sun, 2 Feb 2014 22:35:48 -0500
From:	Jörn Engel <joern@...fs.org>
To:	Theodore Ts'o <tytso@....edu>
Cc:	Stephan Mueller <smueller@...onox.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	macro@...ux-mips.org, ralf@...ux-mips.org, dave.taht@...il.com,
	blogic@...nwrt.org, andrewmcgr@...il.com, geert@...ux-m68k.org,
	tg@...bsd.de
Subject: Re: [PATCH,RFC] random: collect cpu randomness

On Sun, 2 February 2014 20:39:22 -0500, Theodore Ts'o wrote:
> 
> The real question is how much overhead does it add, and is it worth
> it.  Jörn, I take it that was the reason for creating an even faster,
> but weaker mixing function?  Was the existing "fast mix" causing a
> measurable overhead, or was this your just being really paranoid about
> not adding anything to the various kernel fastpaths?

It was paranoia.  And I am still somewhat paranoid and don't trust my
benchmark results yet.  Maybe on an 1024-CPU Altix with a 100k-thread
workload the overhead is too much.  Just because I couldn't measure a
difference on my wimpy notebook does not mean much.

Jörn

--
One of the painful things about our time is that those who feel certainty
are stupid, and those with any imagination and understanding are filled
with doubt and indecision.
-- Bertrand Russell
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