Messages in this thread | | | Subject | Re: [RFC][PATCH] new timeofday arch specific hooks (v. A2) | From | Benjamin Herrenschmidt <> | Date | Wed, 26 Jan 2005 10:53:47 +1100 |
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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.
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