Date: Mon, 8 May 2006 09:05:00 -0500
From: Matt Mackall <mpm@selenic.com>
To: "David S. Miller" <davem@davemloft.net>
Cc: pavel@suse.cz, tytso@mit.edu, mrmacman_g4@mac.com, akpm@osdl.org,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH 7/14] random: Remove SA_SAMPLE_RANDOM from network drivers
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On Mon, May 08, 2006 at 12:07:54AM -0700, David S. Miller wrote:
> From: Pavel Machek <pavel@suse.cz>
> Date: Mon, 8 May 2006 06:26:05 +0000
> 
> > > Then I'll run my test on one of the various arches where HZ=~100 and
> > > we don't have a TSC. Like Sparc?
> > > 
> > >   /* XXX Maybe do something better at some point... -DaveM */
> > >   typedef unsigned long cycles_t;
> > >   #define get_cycles()    (0)
> > 
> > Seems like sparc32 is broken :-(, and probably broken terminally...
> > there are very little randomness sources that can handle 10msec
> > sampling period :-(.
> > 
> > Maybe we should disable /dev/random on sparc32?
> 
> What do other platforms without a TSC do?

Using get_cycles() for /dev/random is new as of 2.6. Before that, we
were directly calling rdtsc on x86 alone. 10msec resolution is fine
for plenty of sources.

>From a brief glance, the following don't have a useful get_cycles:

v850, sh, sh64, h8300, m32r, arm, arm26, cris, frv, um, m68k, xtensa,
sparc

And several others like mips (and x86) have one on only some hardware.

-- 
Mathematics is the supreme nostalgia of our time.
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