Re: CONFIG_PRINTK_TIME woes

[Andrew Morton <akpm@osdl.org>]

Nick Piggin <nickpiggin@yahoo.com.au> wrote:
>
> Andrew Morton wrote:
> 
> > 
> > yup.
> > 
> > 
> >>Why not use something like do_gettimeofday? (or I'm sure one
> >>of our time keepers can suggest the right thing to use).
> > 
> > 
> > do_gettimeofday() takes locks, so a) we can't do printk from inside it and
> 
> Dang, yeah maybe this is the showstopper.
> 
> > b) if you do a printk-from-interupt and the interrupted code was running
> > do_gettimeofday(), deadlock.
> > 
> 
> What about just using jiffies, then?
> 
> Really, sched_clock() is very broken for this (I know you're
> not arguing against that).
>
> It can go backwards when called twice from the same CPU, and the
> number returned by one CPU need have no correlation with that
> returned by another.

jiffies wouldn't have sufficient resolution for this application.  Bear in
mind that this is just a debugging thing - it's better to have good
resolution with occasional theoretical weirdness than to have poor
resolution plus super-consistency, IMO.

> However, I understand you probably just want something quick and
> dirty for 2.6.13 and would be happy just if it isn't more broken
> than before ;)

We're OK for 2.6.13, I think.  ia64 people will quickly learn to not turn
the option on.