linux-kernel - Re: [PATCH,RFC] random: make fast

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Message-ID: <20130923150222.GA13764@logfs.org>
Date:	Mon, 23 Sep 2013 11:02:22 -0400
From:	Jörn Engel <joern@...fs.org>
To:	Theodore Ts'o <tytso@....edu>
Cc:	Jörg-Volker Peetz <jvpeetz@....de>,
	John Stultz <john.stultz@...aro.org>,
	Stephan Mueller <smueller@...onox.de>,
	LKML <linux-kernel@...r.kernel.org>, dave.taht@...ferbloat.net,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH,RFC] random: make fast_mix() honor its name

On Sun, 22 September 2013 22:43:38 -0400, Theodore Ts'o wrote:
> On Sun, Sep 22, 2013 at 08:16:23PM -0400, Jörn Engel wrote:
> > How about we switch between the two mixing functions depending on the
> > interrupt load?  If this CPU has seen fewer than 1000 interrupts in
> > the last second, use the better one, otherwise us the cheaper one?
> 
> I guess the question here is whether it's worth it.  On a 2.8 GHz
> laptop Ivy Bridge chip the numbers are:

Then let us assume for now it is not worth it.  When I finally get
around to generating profiles for my insane system we can revisit the
issue.

> I am very strongly of the opinion that the number of systems where you
> have an embedded system with that kind of inane interrupt rate is the
> 0.00000000001% case.

That would be one machine in 10^13?  I doubt we have reached 10^13
machines running Linux in all of history, so a single example would
defeat your very strong opinion. ;)

Anyway, let me collect some real numbers before we argue any further.
And thank you for your maintainership.  It may not appear that way,
but I have _very_ little to complain about in drivers/char/random.c.

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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