Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods

[Peter Zijlstra]

On Mon, Jul 10, 2017 at 10:27:05AM -0700, Andi Kleen wrote:
> On Mon, Jul 10, 2017 at 06:42:06PM +0200, Peter Zijlstra wrote:

> > I have, and last time I did the actual poking at the LAPIC (to make NOHZ
> > happen) was by far the slowest thing happening.
> 
> That must have been a long time ago because modern systems use TSC deadline
> for a very long time ...  

Its been a while, but I didn't use the very latest chip when I did.

> It's still slow, but not as slow as the LAPIC.

Deadline TSC is a LAPIC timer mode. Sure the MSR might be slightly
cheaper than the MMIO, but its still painful.