Re: BUG: cpufreq notification broken
From: Alan Stern
Date: Thu Nov 16 2006 - 16:56:55 EST
On Thu, 16 Nov 2006, Thomas Gleixner wrote:
> On Thu, 2006-11-16 at 16:26 -0500, Alan Stern wrote:
> > On Thu, 16 Nov 2006, Thomas Gleixner wrote:
> > > There is another issue with this SRCU change:
> > >
> > > The notification comes actually after the real change, which is bad. We
> > > try to make the TSC usable by backing it with pm_timer accross such
> > > states, but this behaviour breaks the safety code.
> > I don't understand. Sending notifications is completely separate from
> > setting up the notifier chain's head. The patch you mentioned didn't
> > touch the code that sends the notifications.
> Yeah, my bad. It just uses rcu based locking, but its still synchronous.
> I have to dig deeper, why the change of the frequency happens _before_
> the notifier arrives.
There are supposed to be _two_ notifier calls: one before the frequency
change and one after. Check the callers of cpufreq_notify_transition().
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