Re: get_cycles() on i386

[Nick Piggin]

Nick Piggin wrote:

> Linus Torvalds wrote:
>
> > On 4 Nov 2003, john stultz wrote:
> >
> > > CONFIG_X86_TSC be the devil. Personally, I'd much prefer dropping the
> > > compile time option and using dynamic detection. Something like (not
> > > recently tested and i believe against 2.5.something, but you get the
> > > idea):
> >
> > Some of the users are really timing-critical (eg scheduler).
>
> The scheduler uses its own sched_clock which only gives jiffies
> resolution if CONFIG_NUMA is defined. Unfortunate because I think
> its interactive behaviour isn't so good with ms resolution.
>
> The scheduler does not need to have synchronised TSCs though, I think.
> It just means 2 more calls to sched_clock in a slow path (smp migration).
Well no, its much trickier than that I think :(



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