Re: Tickless/dyntick kernel, highres timer and general time crapectomy

[Sergei Shtylyov <sshtylyov@ru.mvista.com>]

Hello.

Franck Bui-Huu wrote:

> Actually I'm wondering if we shouldn't create a new file
> "arch/mips/kernel/time2.c" which will be a complete rewrite of the
> old one (interrupt handler, function pointers, clocksource,
> clockevent). This file would be the future replacement of the old
> time.c. This new file would be used only if the board have been
> updated accordingly. That may help to migrate...

    We've been there and done that -- for George Anzinger's HRT. :-)

>>> Another issue I have is to implement clockevent set_mode() method. You
>>> left it empty but I think we need at least to shut down the timer
>>> interrupt when setting the clock event device. Strangely I haven't
>>> found a "generic" way to stop them through cp0. Have I missed
>>> something ?

>> You can mask the count/compare interrupt in the status register like any
>> other interrupt.  Keep in mind that on many CPUs this interrupt is
>> shared with the performance counter interrupt so cannot always be
>> disabled.

> Well this interrupt could be shared with other devices too, couldn't it ?
> If so only the board code can disable it.

>> There is no other disable bit for this interrupt than the IE bit in the
>> status register.  So it may just have to be ignored.

> That would mean we can't have a tickless system in these cases, wouldn't
> it ?

    No, it doesn't. Even on dyntick kernels, interrupts do happen several 
times a second. Dynticks have nothing to do with disabling timer interrupts...

WBR, Sergei