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SubjectRe: Fwd: Commit 76a2a6ee8a0660a29127f05989ac59ae1ce865fa breaks PXA270 (at least)?
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On Wed, 2008-07-30 at 09:10 +0200, Peter Zijlstra wrote:
> On Tue, 2008-07-29 at 23:56 +0100, Russell King - ARM Linux wrote:
> > On Tue, Jul 29, 2008 at 03:46:05PM -0700, Andrew Morton wrote:
> > > On Tue, 29 Jul 2008 23:31:05 +0100
> > > Russell King - ARM Linux <linux@arm.linux.org.uk> wrote:
> > >
> > > > But then some bright spark thought it would be a good idea to get
> > > > rid of printk_clock().
> > >
> > > <does git-log, searches for printk_clock>
> > >
> > > commit 86faf39d0fc04272b05fab1db6d683f3ac7199d1
> > > Author: Ingo Molnar <mingo@elte.hu>
> > > Date: Fri Jan 25 21:07:59 2008 +0100
> > >
> > > sched: remove printk_clock references from ia64
> > >
> > > remove remaining printk_clock references from ia64.
> > >
> > > Signed-off-by: Ingo Molnar <mingo@elte.hu>
> > >
> > > commit b842271fbb9c8b5fd0e1c3e1895a3b67ba5bcc54
> > > Author: Ingo Molnar <mingo@elte.hu>
> > > Date: Fri Jan 25 21:07:59 2008 +0100
> > >
> > > sched: remove printk_clock()
> > >
> > > printk_clock() is obsolete - it has been replaced with cpu_clock().
> > >
> > > Signed-off-by: Ingo Molnar <mingo@elte.hu>
> > >
> > >
> > > That's it? It rates a 0.5/10 for changelogging :(
> > >
> > > Looking further on...
> > >
> > > commit e97126cd9056b3b42cdc862ace2ed66f8026f55b
> > > Author: Russell King <rmk@dyn-67.arm.linux.org.uk>
> > > Date: Mon Jan 8 19:49:12 2007 +0000
> > >
> > > [ARM] Provide basic printk_clock() implementation
> > >
> > > Current sched_clock() implementations on ARM cause unbootable kernels
> > > with PRINTK_TIME support enabled. To avoid this, provide a basic
> > > printk_clock() implementation which avoids sched_clock() being called
> > > before the page tables have been set up.
> > >
> > >
> > > which I assume is why arm is crashing again?
> >
> > Precisely - Ingo has effectively progressively backed out my bug fix
> > in a round-about manner by making printk require a working sched_clock
> > again.
> >
> > > Really, I think arch-overrideable printk_clock() was a good idea.
> > > printk is just _special_. It's called wildly early and it is called in
> > > all conceivable contexts and it just must work no matter what. It's
> > > totally understandable that an architecture would need to override
> > > printk's timestamp generator.
> >
> > That's one solution, the other is to have that commit reverted. I
> > don't really mind which, only that we have a solution ASAP so that
> > the current popular ARM SoCs have a bootable kernel again.
>
> Can't you make sched_clock() return 0 when its called before its up and
> running? Otherwise -

> perhaps you can play with the location of
> sched_clock_init(). cpu_clock() will return 0 before that.

Sorry - that's only relevant for HAVE_UNSTABLE_SCHED_CLOCK and x86 seems
to be the only one using that (which just shows the platforms quality
</sarcasm>).





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