Re: [RFC PATCH 0/5] futex: introduce an optimistic spinning futex

On Wed, 2014-07-23 at 08:57 +0200, Peter Zijlstra wrote: 

On Wed, Jul 23, 2014 at 06:55:03AM +0200, Mike Galbraith wrote:

quoted

On Mon, 2014-07-21 at 09:42 -0700, Andi Kleen wrote:

quoted

FWIW the main problem is currently that switch-through-idle is so 
slow. I think improving that would give a boost to far more
situations.

Two high frequency idle enter/exit suckage spots:

1) nohz (tick) - it's expensive to start/stop tick on every micro-idle,
throttle it or something.

Yeah, so the idea was to use the cpuidle idle guestimator to control
this, and now that we've moved it somewhat closer to the scheduler that
might become possible.

quoted

2) ondemand governor - tweak silly default settings to reflect the
reality that we routinely schedule communicating threads cross core.

Yeah, so the plan is to shoot cpufreq in the head and base the
replacement on smp aware metrics ;-) Its on a todo list somewhere..

It never ceases to amaze me that people aren't screaming bloody murder
about those two spots.  Watching performance of lightly loaded boxen is
enough to make a grown man cry.

SUSE (and I in all of my many regression testing trees) puts tourniquets
on both of these blood spurting gashes, laptops be damned.

I also resurrect mwait_idle(), as while you may consider it obsolete, I
still love my lovely little Q6600 box (power sucking pig) dearly :)

-Mike