linux-kernel - Re: RFC: Ideal Adaptive Spinning Conditions

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Date:	Sat, 03 Apr 2010 14:00:15 -0400
From:	john cooper <john.cooper@...rd-harmonic.com>
To:	Darren Hart <dvhltc@...ibm.com>
CC:	"Peter W. Morreale" <pmorreale@...ell.com>, rostedt@...dmis.org,
	"lkml," <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Gregory Haskins <ghaskins@...ell.com>,
	Sven-Thorsten Dietrich <sdietrich@...ell.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Chris Mason <chris.mason@...cle.com>,
	john cooper <john.cooper@...hat.com>
Subject: Re: RFC: Ideal Adaptive Spinning Conditions

Darren Hart wrote:
> Right, and I'm looking to provide some kernel assistance for userspace
> spinlocks here, and am targeting short lived critical sections as well.

What did you have in mind beyond existing mechanisms
which address sibling contention?

One scenario which AFAICT isn't yet addressed is that
of a userspace spin lock holder taking a scheduling
preemption which may result in other threads piling up
on the lock orders of magnitude beyond normal wait times,
until the lock holder is rescheduled.  

-john

-- 
john.cooper@...rd-harmonic.com
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