From: Stephan Mueller <smueller@chronox.de>
To: "Theodore Ts'o" <tytso@mit.edu>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
LKML <linux-kernel@vger.kernel.org>,
dave.taht@bufferbloat.net
Subject: Re: [PATCH] /dev/random: Insufficient of entropy on many architectures
Date: Wed, 11 Sep 2013 08:49:49 +0200 [thread overview]
Message-ID: <2947789.S63SVUbC3N@tauon> (raw)
In-Reply-To: <20130910211454.GJ29237@thunk.org>
Am Dienstag, 10. September 2013, 17:14:54 schrieb Theodore Ts'o:
Hi Theodore,
>On Tue, Sep 10, 2013 at 10:48:00PM +0200, Geert Uytterhoeven wrote:
>> So the first importance for random_get_fast_cycles() is that it needs
>> to be fast. What's most important next: number of bits or
>> high-frequency?
>High-frequency. For example MIPS has a register which is bumped at
>every clock tick, modulo the number of lines in the TLB. That's what
>we're probably going to end up using for MIPS, on the assumption that
>the time between interrupts is not likely going to be related to the
>number of lines in the TLB. :-)
>
>Something like jiffies has lots of bits, but since it's updated at a
>much slower rate, it's not as useful if we are trying to measure
>uncertainity based on the interrupt time. (Worse yet, depending on
>how the architecture handles the clock, there mgiht be a very high
>correlation between when the jiffies counter gets incremented and the
>timer interrupt....)
>
>And yes, we will need to make sure this gets well documented in the
>sources when we introduce random_get_fast_cycles()....
As general hunch on the speed, I would say is a simple test that two
adjacent calls to obtain a time stamp show a delta. Eg.
__u64 tmp = random_get_fast_cycles() - random_get_fast_cycles();
if(0 == tmp)
return fail;
return pass;
>
>Cheers,
>
> - Ted
Ciao
Stephan
next prev parent reply other threads:[~2013-09-11 6:50 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-10 11:31 Stephan Mueller
2013-09-10 11:46 ` Geert Uytterhoeven
2013-09-10 15:04 ` Theodore Ts'o
2013-09-10 16:54 ` Stephan Mueller
2013-09-10 18:25 ` Theodore Ts'o
2013-09-10 19:15 ` Stephan Mueller
2013-10-10 6:50 ` Pavel Machek
2013-10-14 21:13 ` Theodore Ts'o
2013-09-10 20:48 ` Geert Uytterhoeven
2013-09-10 21:14 ` Theodore Ts'o
2013-09-11 6:49 ` Stephan Mueller [this message]
2013-09-12 11:59 ` Geert Uytterhoeven
2013-09-12 12:08 ` Stephan Mueller
2013-09-12 12:15 ` Geert Uytterhoeven
2013-09-12 12:35 ` Stephan Mueller
2013-09-12 12:47 ` Geert Uytterhoeven
2013-09-12 12:57 ` Stephan Mueller
2013-09-12 21:18 ` Jörn Engel
2013-09-13 11:33 ` Thorsten Glaser
2013-09-12 14:25 ` Theodore Ts'o
2013-09-10 19:38 ` John Stultz
2013-09-10 19:44 ` John Stultz
2013-09-10 19:47 ` Stephan Mueller
2013-09-10 20:35 ` John Stultz
2013-09-10 20:38 ` Theodore Ts'o
2013-09-10 20:46 ` John Stultz
2013-09-10 21:10 ` Theodore Ts'o
2013-09-10 22:08 ` John Stultz
2013-09-10 22:33 ` Theodore Ts'o
2013-09-11 0:31 ` John Stultz
2013-09-11 0:50 ` Theodore Ts'o
2013-09-11 1:14 ` John Stultz
2013-09-12 20:46 ` H. Peter Anvin
2013-09-12 21:07 ` Jörn Engel
2013-09-12 23:31 ` Theodore Ts'o
2013-09-12 23:35 ` Jörn Engel
2013-09-13 0:00 ` Jörn Engel
2013-09-16 15:40 ` [PATCH,RFC] random: make fast_mix() honor its name Jörn Engel
2013-09-21 21:25 ` Theodore Ts'o
2013-09-21 21:41 ` Theodore Ts'o
2013-09-22 3:05 ` Theodore Ts'o
2013-09-22 21:01 ` Jörg-Volker Peetz
2013-09-22 21:27 ` Theodore Ts'o
2013-09-22 20:53 ` Jörn Engel
2013-09-22 23:36 ` Theodore Ts'o
2013-09-23 0:16 ` Jörn Engel
2013-09-23 2:43 ` Theodore Ts'o
2013-09-23 15:02 ` Jörn Engel
2013-09-23 7:39 ` Jörg-Volker Peetz
2013-09-22 20:31 ` Jörn Engel
2013-09-22 20:14 ` Jörn Engel
2013-09-12 21:31 ` [PATCH] /dev/random: Insufficient of entropy on many architectures Jörn Engel
2013-09-13 5:36 ` Stephan Mueller
2013-09-13 11:54 ` Thorsten Glaser
2013-09-13 19:29 ` Theodore Ts'o
2013-09-13 15:26 ` Jörn Engel
2013-09-13 18:59 ` Theodore Ts'o
2013-09-15 11:12 ` Stephan Mueller
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