linux-kernel - Re: [RFC PATCH v2] Implement Batched (group) ticket lock

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Message-ID: <20140701095521.GO6758@twins.programming.kicks-ass.net>
Date:	Tue, 1 Jul 2014 11:55:21 +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, riel@...hat.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, mtosatti@...hat.com,
	chegu_vinod@...com
Subject: Re: [RFC PATCH v2] Implement Batched (group) ticket lock

On Tue, Jul 01, 2014 at 03:14:09PM +0530, Raghavendra K T wrote:
> On 07/01/2014 01:35 PM, Peter Zijlstra wrote:
> >On Sat, Jun 28, 2014 at 02:47:04PM +0530, Raghavendra K T wrote:
> >>In virtualized environment there are mainly three problems
> >>related to spinlocks that affects performance.
> >>1. LHP (lock holder preemption)
> >>2. Lock Waiter Preemption (LWP)
> >>3. Starvation/fairness
> >>
> >>Though Ticketlocks solve fairness problem it worsens LWP, LHP problems. Though
> >>pv-ticketlocks tried to address these problems we can further improve at the
> >>  cost of relaxed fairness. The following patch tries to achieve that by grouping
> >>(batched) ticketlocks.
> >
> >And here I stop reading and ignore this patch, right?
> >
> >Why should I look at this?
> >
> 
> For baremetal we continue to have 'fully fair ticketlock' with this patch
> series.
> 

But but but, we're looking at removing ticket locks. So why do we want
to invest in them now?
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