Re: [PATCH v4] printk: Add monotonic, boottime, and realtime timestamps

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Tue, Aug 08, 2017 at 07:08:00PM -0400, Prarit Bhargava wrote:
> 
> 
> On 08/08/2017 04:28 AM, Peter Zijlstra wrote:
> > On Mon, Aug 07, 2017 at 01:36:39PM -0700, Paul E. McKenney wrote:
> >> On Mon, Aug 07, 2017 at 04:06:09PM -0400, Prarit Bhargava wrote:
> > 
> >>> peterz?  Want to offer a suggestion?  The issue is that I'm changing a bool
> >>> config option to an int and that impacts all the arch's defconfigs.  John points
> >>> out that this is a lot of churn and we're both wondering if there's a better way
> >>> to do the configs.
> >>
> >> The usual approach is to keep the old bool Kconfig option, and add another
> >> int Kconfig option that depends on the original one.  The tests for
> >> the int value get a bit more complex, but one way to handle this is to
> >> define a cpp macro something like the following:
> >>
> >> #ifdef CONFIG_OLD_OPTION
> >> #define CPP_NEW_OPTION 0
> >> #else
> >> #define CPP_NEW_OPTION CONFIG_NEW_OPTION
> >> #endif
> >>
> >> Then use CPP_NEW_OPTION, where zero means disabled and other numbers
> >> select the available options.
> >>
> >> Adjust to suit depending on what values mean what.
> >>
> >> Another approach is to make the range of the new Kconfig option
> >> depend on the old option:
> >>
> >> config NEW_OPTION
> >> 	int "your description here"
> >> 	range 1 5 if OLD_OPTION
> >> 	range 0 0 if !OLD_OPTION
> >> 	default 0
> >> 	help
> >> 	  your help here
> >>
> >> Again, adjust to suit depending on what values mean what.
> > 
> > Right this. Except I don't see the !OLD_OPTION working as expected.
> > A 'new' config will not include the old one, so the !OLD_OPTION thing
> > will 'always' be true.
> > 
> > So your:
> > 
> >> @@ -1,8 +1,46 @@
> >>  menu "printk and dmesg options"
> >>
> >> +choice
> >> +       prompt "printk default clock"
> >> +       config PRINTK_TIME_DISABLE
> >> +       bool "Disabled"
> >> +       help
> >> +        Selecting this option disables the time stamps of printk().
> >> +
> >> +       config PRINTK_TIME_LOCAL
> >> +       bool "Local Clock"
> >> +       help
> >> +         Selecting this option causes the time stamps of printk() to be
> >> +         stamped with the unadjusted hardware clock.
> >> +
> >> +       config PRINTK_TIME_BOOT
> >> +       bool "CLOCK_BOOTTIME"
> >> +       help
> >> +         Selecting this option causes the time stamps of printk() to be
> >> +         stamped with the adjusted boottime clock.
> >> +
> >> +       config PRINTK_TIME_MONO
> >> +       bool "CLOCK_MONOTONIC"
> >> +       help
> >> +         Selecting this option causes the time stamps of printk() to be
> >> +         stamped with the adjusted monotonic clock.
> >> +
> >> +       config PRINTK_TIME_REAL
> >> +       bool "CLOCK_REALTIME"
> >> +       help
> >> +         Selecting this option causes the time stamps of printk() to be
> >> +         stamped with the adjusted realtime clock.
> >> +
> >> +endchoice
> >> +
> >>  config PRINTK_TIME
> > 
> > Change that into something like:
> > 
> > config PRINTK_CLOCK
> > 
> > 
> >> -       bool "Show timing information on printks"
> >> +       int "Show time stamp information on printks"
> >>         depends on PRINTK
> >> +       default 0 if PRINTK_TIME_DISABLE
> >> +       default 1 if PRINTK_TIME_LOCAL
> > 
> > And that into:
> > 
> > 	default 1 if PRINTK_TIME_LOCAL || PRINTK_TIME
> > 
> >> +       default 2 if PRINTK_TIME_BOOT
> >> +       default 3 if PRINTK_TIME_MONO
> >> +       default 4 if PRINTK_TIME_REAL
> >> 	  help
> >> 	    Selecting this option causes time stamps of the printk()
> > 
> > Then the old PRINTK_TIME symbol will auto-convert into the new
> > equivalent.
> > 
> 
> I don't think there's an easy code way around this.  Essentially this Kconfig
> code boils down to properly evaluating
> 
> config PRINTK_CLOCK
> 	default 1 if PRINTK_TIME
> 	default 0
> 
> where there is no Kconfig entry for PRINTK_TIME.
> 
> If undefined CONFIG_PRINTK_TIME is used in a config, it is immediately
> scrubbed by the kconfig script so it doesn't "exist" when CONFIG_PRINTK_CLOCK
> is evaluated.  The result of that is CONFIG_PRINT_CLOCK=0.
> 
> I tried
> 
> config PRINTK_TIME
> 	bool "old config option"
> 
> then I end up with both a CONFIG_PRINTK_CLOCK=1 and a CONFIG_PRINTK_TIME=y in
> the resulting config which is confusing.
> 
> I've debated using the other suggestion that Paul made but TBH (sorry
> Paul) it seems like I'm avoiding the real but noisy solution of
> 
> 	s/PRINTK_TIME=y/PRINTK_TIME=1/g
> 
> I'm obviously open to other suggestions...

It is someone else's turn to provide a suggestion.  ;-)

							Thanx, Paul