linux-kernel - Re: random(4) changes

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Message-ID: <20160425173825.GB13997@two.firstfloor.org>
Date:	Mon, 25 Apr 2016 10:38:25 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Stephan Mueller <smueller@...onox.de>
Cc:	Andi Kleen <andi@...stfloor.org>,
	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

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

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.