Re: [RFC][PATCH] new timeofday arch specific hooks (v. A2)

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Tue, 2005-01-25 at 15:09 -0800, john stultz wrote:

> The performance is a concern, and right now there are issues (ntp_scale
> being the top of the list) however I hope they can be resolved. Looking
> at ppc64's do_gettimeofday() vs this implementation there we do have
> more overhead, but maybe you could suggest how we can avoid some of it?

I would suggest reclaculating the scale factor and offset for ntp
adjustement regulary from the timer tick or so, not on each gettimeofday
call.

Also, I have some updates to the ppc64 implementation where I regulary
update the pre-scale offset into the post-scale one so that the
timebase-prescale substraction always gives a 32 bits number. I do that
so my fast userland gettimeofday can be implemented more easily and more
efficiently for 32 bits processes. I yet have to check how I can hook
those things into your new scheme.

> I still want to support vsyscall gettimeofday, although it does have to
> be done on an arch-by-arch basis. It's likely the systemcfg data
> structure can still be generated and exported. I'll look into it and see
> what can be done.

Well, since it only contains the prescale and postscale offsets and the
scaling value, it only needs to be updated when they change, so a hook
here would be fine.

Ben.