linux-kernel - Re: random(4) changes

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Message-ID: <7735834.PWhNOHfhKX@positron.chronox.de>
Date:	Mon, 25 Apr 2016 19:56:17 +0200
From:	Stephan Mueller <smueller@...onox.de>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Sandy Harris <sandyinchina@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-crypto@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
	Jason Cooper <jason@...edaemon.net>,
	John Denker <jsd@...n.com>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: random(4) changes

Am Montag, 25. April 2016, 10:38:25 schrieb Andi Kleen:

Hi Andi,

> On Mon, Apr 25, 2016 at 07:25:55PM +0200, Stephan Mueller wrote:
> > Am Montag, 25. April 2016, 09:06:03 schrieb Andi Kleen:
> > 
> > Hi Andi,
> > 
> > > Sandy Harris <sandyinchina@...il.com> writes:
> > > 
> > > There is also the third problem of horrible scalability of /dev/random
> > > output on larger systems, for which patches are getting ignored.
> > > 
> > > https://lkml.org/lkml/2016/2/10/716
> > > 
> > > Ignoring problems does not make them go away.
> > 
> > I have seen your patches, but I am not fully sure I understand the root
> > cause. is the noise source handling the issue or the random number
> > generation the issue?
> 
> Noise source handling is fine, the problem is the global locking on the
> entropy pools when generating random numbers.
> 
> > If it is the latter, can you explain where the scalability issue comes in?
> 
> A single pool which is locked/written to does not scale. Larger systems
> need multiple pools

That would imply that even when you have a system with 1000 CPUs, you want to 
have a large amount of random numbers. Is this the use case?

Or is simply the presence of 1000 CPUs an issue for "normal" loads on 
/dev/urandom?
> 
> -Andi


Ciao
Stephan