linux-kernel - Re: [RFC] Implement Batched (group) ticket lock

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Message-ID: <20140529064606.GH19143@laptop.programming.kicks-ass.net>
Date:	Thu, 29 May 2014 08:46:06 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
Cc:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	konrad.wilk@...cle.com, pbonzini@...hat.com, gleb@...hat.com,
	paulmck@...ux.vnet.ibm.com, torvalds@...ux-foundation.org,
	waiman.long@...com, davej@...hat.com, oleg@...hat.com,
	x86@...nel.org, jeremy@...p.org, paul.gortmaker@...driver.com,
	ak@...ux.intel.com, jasowang@...hat.com, fernando_b1@....ntt.co.jp,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	xen-devel@...ts.xenproject.org, riel@...hat.com,
	mtosatti@...hat.com, chegu_vinod@...com
Subject: Re: [RFC] Implement Batched (group) ticket lock

On Wed, May 28, 2014 at 05:46:39PM +0530, Raghavendra K T wrote:
> In virtualized environment there are mainly three problems
> related to spinlocks that affect performance.
> 1. LHP (lock holder preemption)
> 2. Lock Waiter Preemption (LWP)
> 3. Starvation/fairness
> 
>  Though ticketlocks solve the fairness problem, it worsens LWP, LHP problems.
> pv-ticketlocks tried to address this. But we can further improve at the
> cost of relaxed fairness.

So I really hate the idea of having different locks for paravirt and
normal kernels.

And we're looking to move to that queued lock for normal kernels.
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