Re: [PATCH 1/3] dynticks - implement no idle hz for x86

[Nishanth Aravamudan <nacc@us.ibm.com>]

On 05.09.2005 [09:58:59 +0300], Tony Lindgren wrote:
> * Nishanth Aravamudan <nacc@us.ibm.com> [050904 23:38]:
> > On 04.09.2005 [21:26:16 +0100], Russell King wrote:
> > > On Sun, Sep 04, 2005 at 01:10:54PM -0700, Nishanth Aravamudan wrote:
> > > > I've got a few ideas that I think might help push Con's patch coalescing
> > > > efforts in an arch-independent fashion.
> > > 
> > > Note that ARM contains cleanups on top of Tony's original work, on
> > > which the x86 version is based.
> > > 
> > > Basically, Tony submitted his ARM version, we discussed it, fixed up
> > > some locking problems and simplified it (it contained multiple
> > > structures which weren't necessary, even in multiple timer-based systems).
> > 
> > Make sense. Thanks for the quick feedback!
> > 
> > > I'd be really surprised if any architecture couldn't use what ARM has
> > > today - in other words, this is the only kernel-side interface:
> > > 
> > > #ifdef CONFIG_NO_IDLE_HZ
> > > 
> > > #define DYN_TICK_SKIPPING       (1 << 2)
> > > #define DYN_TICK_ENABLED        (1 << 1)
> > > #define DYN_TICK_SUITABLE       (1 << 0)
> > > 
> > > struct dyn_tick_timer {
> > >         unsigned int    state;                  /* Current state */
> > >         int             (*enable)(void);        /* Enables dynamic tick */
> > >         int             (*disable)(void);       /* Disables dynamic tick */
> > >         void            (*reprogram)(unsigned long); /* Reprograms the timer */
> > >         int             (*handler)(int, void *, struct pt_regs *);
> > > };
> > > 
> > > void timer_dyn_reprogram(void);
> > > #else
> > > #define timer_dyn_reprogram()   do { } while (0)
> > > #endif
> > 
> > That looks great! So I guess I'm just suggesting moving this from
> > include/asm-arch/mach/time.h to arch-independent headers? Perhaps
> > timer.h is the best place for now, as it already contains the
> > next_timer_interrupt() prototype (which probably should be in the #ifdef
> > with timer_dyn_reprogram()).
> 
> Yes, the above should be enough on all platforms. I believe x86 still uses
> two structs, and should be updated to use the interface above. There are
> some extra state flags on x86, but even some of those might be
> unnecessary now.

Yes, I agree.

> It may not be obvious from the mailing list discussions, but really the
> remaining problems are to fix the x86 legacy issues with all the timers,
> not with the interface.

The interface in x86 is fine, I agree. But the problem I see, is that we
would now have *3* different implementations of dyn-tick. At the point
where Con or anyone else is ready to propose merging of the code, I
think the dyn-tick work comes across much better if it simultaneously
unifies the existing NO_IDLE_HZ implementations in common files where
appropriate.

Thanks,
Nish