Question on timekeeping subsystem

Question on timekeeping subsystem

[Francis Moreau]

Hello,

I looked at this subsystem, trying to understand how this works on Linux
but call me a dumb xxx but I think I really miss something.

First I tried to find some documentation on the current implementation
but haven't found any thing really usefull. Specially there's nothing about
it in Documentation/ directory. Please correct me if I'm already wrong.

Actually I read the implementation of update_wall_time() and I really fail
to understand how it works. This is probably because I don't know
what "xtime_nsec" and "error" fields in clocksource struct are for.
These fields are not documented anywhere in the source code so it
should be obvious but unfortunately not for me.

Another example almost the first thing done by this function is:

    clock->xtime_nsec += (s64)xtime.tv_nsec << clock->shift;

What's the hell this ?

I know I'm stupid but please enlight me ;)

Thanks
-- 
Francis

Re: Question on timekeeping subsystem

[Roman Zippel]

Hi,

On Wednesday 13. February 2008, Francis Moreau wrote:

> First I tried to find some documentation on the current implementation
> but haven't found any thing really usefull. Specially there's nothing about
> it in Documentation/ directory. Please correct me if I'm already wrong.
>
> Actually I read the implementation of update_wall_time() and I really fail
> to understand how it works. This is probably because I don't know
> what "xtime_nsec" and "error" fields in clocksource struct are for.
> These fields are not documented anywhere in the source code so it
> should be obvious but unfortunately not for me.

These mails should help to understand, what this code does:

http://lkml.org/lkml/2006/3/4/61
http://lkml.org/lkml/2006/4/3/205

bye, Roman

Re: Question on timekeeping subsystem

[Francis Moreau]

Hello Roman,

On Thu, Feb 14, 2008 at 2:37 AM, Roman Zippel <zippel@linux-m68k.org> wrote:
>
>  These mails should help to understand, what this code does:
>
>  http://lkml.org/lkml/2006/3/4/61
>  http://lkml.org/lkml/2006/4/3/205
>

Indeed !

They look interesting after a quick look but I haven't time yet to
read them carefully.

Thanks
-- 
Francis