Re: [discuss] Re: [PATCH] x86-64: Fix bad assumption that dualcorecpus have synced TSCs

[Andrew Morton]

Andi Kleen <ak@xxxxxxx> wrote:
>
> On Wed, Sep 21, 2005 at 10:15:08AM -0500, Ray Bryant wrote:
> > On Tuesday 20 September 2005 23:03, Daniel Jacobowitz wrote:
> > 
> > >
> > > FYI, at least I have reproduced this without powernow loaded.
> > 
> > There are cases that we are aware of where the TSC will count slower while the 
> > processor is halted.    This can make TSC's get out of sync on dual cores.

You mean a single `hlt' instruction?   I guess that rules out resyncing them.

> Ok thanks for the confirmation. I guess John's patch is ok then.
> Drawback is much slower to extremly slow gettimeofday  (depending
> if the chipset/BIOS has usable HPET, most seem not to) 

That's a really big drawback.   Will this affect many CPU types?

If the user was prepared to use `idle=poll' then they could get their fast
gettimeofday() back, perhaps.

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