Re: [PATCH] Fix CONFIG_PRINTK_TIME hangs on some systems

[Tony Lindgren <tony@atomide.com>]

* Luck, Tony <tony.luck@intel.com> [060504 09:14]:
> > This issue has been discussed earlier on LKML, but AFAIK
> > there has not been any better solution available:
> > 
> > http://lkml.org/lkml/2005/8/18/173
> 
> I thought that this had been fixed:
> 
> ia64 now has a "printk_clock()" defined in arch/ia64/kernel/time.c
> which overrides the "weak" symbol defined in kernel/printk.c.  This
> calls ia64_printk_clock() ... which defaults to a jiffie based
> routine, but might be an ITC based routine if running on a system
> where the clocks do not drift on different cpus.  Platform code
> can also override this function pointer (which SGI does in their
> sn_setup() routine).
> 
> The ITC based routine still uses sched_clock(), but tries to avoid
> the original problems by not calling sched_clock() until the MMU
> has been set up to map the per-cpu areas (checks whether one of the
> AR.K registers has been set).  Most of this in commit:
> 
>   http://tinyurl.com/ltexa

Thanks, I had missed that patch.

I still think the current printk_clock() approach is broken by
default on an unknown number of platforms.

Probably the best way to fix it would be to make it use jiffies
unless the platform registers a proper printk_clock() function.
 
> Do you still see a problem on some platform?

Yes, on various OMAP boards when 32KHz timer is being used. The 32KHz
timer is not enabled until in timer_init().

Regards,

Tony