linux-kernel - Re: 2.6.23-rc2-mm1: rcutorture xtime usage

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Message-Id: <20070809190623.f60dcf70.akpm@linux-foundation.org>
Date:	Thu, 9 Aug 2007 19:06:23 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Adrian Bunk <bunk@...nel.org>, Josh Triplett <josh@...nel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: 2.6.23-rc2-mm1: rcutorture xtime usage

On Thu, 9 Aug 2007 19:00:40 -0700 "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:

> On Fri, Aug 10, 2007 at 03:31:46AM +0200, Adrian Bunk wrote:
> > On Thu, Aug 09, 2007 at 01:51:06AM -0700, Andrew Morton wrote:
> > >...
> > > Changes since 2.6.23-rc2-mm1:
> > >...
> > > +allow-rcutorture-to-handle-synchronize_sched.patch
> > >...
> > >  2.6.23 queue
> > >...
> > 
> > All drivers were converted to no longer use xtime directly since it 
> > might be quite outdated, but this patch adds a usage of xtime.tv_nsec
> > as RNG...
> 
> This code doesn't care if the time is outdated, as it is simply
> periodically perturbing an RNG, but OK.
> 
> So, what interface are we supposed to be using instead?  I cannot use
> get_random_bytes() due to locking issues.  This is not a cryptographically
> secure usage, so the perturbation does not need to be extremely high
> quality.
> 
> On x86, I would just grab the low-order bits of the TSC, but all of the
> world is not an x86.  ;-)
> 

One used to use sched_clock() for this, then get frowned at.  Now we
have cpu_clock()...
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