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

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Date:	Wed, 23 Jul 2014 06:55:03 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Waiman Long <Waiman.Long@...com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Darren Hart <dvhart@...ux.intel.com>,
	Davidlohr Bueso <davidlohr@...com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	linux-doc@...r.kernel.org, Jason Low <jason.low2@...com>,
	Scott J Norton <scott.norton@...com>
Subject: Re: [RFC PATCH 0/5] futex: introduce an optimistic spinning futex

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

> 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.

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

(3. seek/destroy fastpath cycles, damn things multiply over time)

-Mike

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