On Mon, Jul 10, 2017 at 06:42:06PM +0200, Peter Zijlstra wrote: > On Mon, Jul 10, 2017 at 07:46:09AM -0700, Andi Kleen wrote: > > > So how much of the gain is simply due to skipping NOHZ? Mike used to > > > carry a patch that would throttle NOHZ. And that is a _far_ smaller and > > > simpler patch to do. > > > > Have you ever looked at a ftrace or PT trace of the idle entry? > > > > There's just too much stuff going on there. NOHZ is just the tip > > of the iceberg. > > 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 ... It's still slow, but not as slow as the LAPIC. > Data to indicate what hurts how much would be a very good addition to > the Changelogs. Clearly you have some, you really should have shared. Aubrey? -Andi