From: "H. Peter Anvin" <hpa@zytor.com>
To: Venkatesh Pallipadi <venki@google.com>
Cc: Jarod Wilson <jarod@redhat.com>,
linux-crypto@vger.kernel.org, Matt Mackall <mpm@selenic.com>,
Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
John Stultz <johnstul@us.ibm.com>,
Herbert Xu <herbert@gondor.hengli.com.au>,
"David S. Miller" <davem@davemloft.net>,
Suresh Siddha <suresh.b.siddha@intel.com>
Subject: Re: [PATCH 4/5] tsc: wire up entropy generation function
Date: Mon, 13 Jun 2011 15:36:20 -0700 [thread overview]
Message-ID: <4DF690E4.1060004@zytor.com> (raw)
In-Reply-To: <BANLkTin=BkfyPjaWRc1rfTWU34NLdn7FLgY6yUbSrjzPpx7Gmg@mail.gmail.com>
On 06/13/2011 03:27 PM, Venkatesh Pallipadi wrote:
> On Mon, Jun 13, 2011 at 3:06 PM, Jarod Wilson <jarod@redhat.com> wrote:
>> TSC is high enough resolution that we can use its low-order byte to
>> stir new data into the random number generator entropy pool.
>
> From what I vaguely remember from years past, rdtsc, especially last
> few bits of it are not very good as random number source. As they are
> based on lower bus frequency and a multiplier. May be things have
> changed these days. Adding Peter and Suresh for comments.
This is correct; at the very least I would multiply the low 32 bits of
the TSC with a 32-bit prime number before mixing.
However, the big issue with this is that it's recursive... what causes
this to be invoked... probably an interrupt, which is going to have been
invoked by a timer, quite possible the TSC deadline timer. Oops.
-hpa
next prev parent reply other threads:[~2011-06-13 22:36 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-13 22:06 [PATCH 0/5] Feed entropy pool via high-resolution clocksources Jarod Wilson
2011-06-13 22:06 ` [PATCH 1/5] random: add new clocksource entropy interface Jarod Wilson
2011-06-13 22:06 ` [PATCH 2/5] clocksource: add support for entropy-generation function Jarod Wilson
2011-06-17 20:52 ` Thomas Gleixner
2011-06-17 21:19 ` Jarod Wilson
2011-06-13 22:06 ` [PATCH 3/5] hpet: wire up entropy generation function Jarod Wilson
2011-06-13 22:06 ` [PATCH 4/5] tsc: " Jarod Wilson
2011-06-13 22:27 ` Venkatesh Pallipadi
2011-06-13 22:35 ` Jarod Wilson
2011-06-13 22:36 ` H. Peter Anvin [this message]
2011-06-13 23:10 ` Matt Mackall
2011-06-14 18:11 ` H. Peter Anvin
2011-06-14 0:39 ` Kent Borg
2011-06-14 1:47 ` H. Peter Anvin
2011-06-14 12:39 ` Kent Borg
2011-06-14 14:33 ` Matt Mackall
2011-06-14 17:48 ` Kent Borg
2011-06-14 18:00 ` Matt Mackall
2011-06-14 20:04 ` Kent Borg
2011-06-14 21:04 ` Matt Mackall
2011-06-14 14:02 ` Jarod Wilson
2011-06-13 23:55 ` Kent Borg
2011-06-17 20:58 ` Thomas Gleixner
2011-06-13 22:06 ` [PATCH 5/5] misc: add clocksource-based entropy generation driver Jarod Wilson
2011-06-17 21:01 ` Thomas Gleixner
2011-06-13 22:38 ` [PATCH 0/5] Feed entropy pool via high-resolution clocksources john stultz
2011-06-14 14:25 ` Jarod Wilson
2011-06-13 23:15 ` Matt Mackall
2011-06-14 15:18 ` Jarod Wilson
2011-06-14 15:22 ` Jarod Wilson
2011-06-14 17:13 ` Matt Mackall
2011-06-14 20:17 ` Jarod Wilson
2011-06-14 21:45 ` Matt Mackall
2011-06-14 22:51 ` Jarod Wilson
2011-06-14 23:12 ` Matt Mackall
2011-06-15 14:49 ` Jarod Wilson
2011-06-15 20:06 ` Matt Mackall
2011-06-17 18:51 ` Jarod Wilson
2011-06-17 19:29 ` Neil Horman
2011-06-17 20:46 ` Matt Mackall
2011-06-17 19:48 ` hpas
2011-06-17 20:28 ` Matt Mackall
2011-06-18 22:40 ` H. Peter Anvin
2011-06-19 13:38 ` Neil Horman
2011-06-19 15:07 ` Herbert Xu
2011-06-20 0:01 ` H. Peter Anvin
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