Re: [RFC][PATCH] Introduce CLOCK_REALTIME_COARSE

[Josh Triplett]

On Mon, Jul 20, 2009 at 03:49:14PM +0200, Peter Zijlstra wrote:
> On Mon, 2009-07-20 at 06:33 -0700, Arjan van de Ven wrote:
> > > Maybe power64, sparc64 and s390x qualify, but certainly nothing on x86
> > > does.
> > 
> > the x86 on my desk disagrees.
> 
> >From what I know even nehalem doesn't have fully synced tscs when your
> machine is large enough, and the timers are still a tad expensive.

All single-socket Nehalem boards have synced TSCs, and some multi-socket
Nehalem boards have synced TSCs, notably Intel's.  I don't know if you
can safely rely on the latter, though.

> Maybe your desktop is next-gen? 't would be nice to finally have an x86
> that has usable clock and timer hardware.

x86 CPUs with the ARAT feature ("always running APIC timer") will let
you use the local APIC even in deep C-states.  I don't know about the
overhead of the local APIC.

- Josh Triplett
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