Re: 2.6.23-rc2-mm1: rcutorture xtime usage

Andrew Morton
2007-08-10T02:06:48Z

On Thu, 9 Aug 2007 19:00:40 -0700 "Paul E. McKenney" <paulmck@linux.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 might be quite outdated, but this patch adds a usage of xtime.tv_nsec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 This code doesn't care if the time is outdated, as it is simply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()...