linux-kernel - Re: [PATCH v2] powerpc ticket locks

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Message-ID: <20140211104030.GG2107@lst.de>
Date:	Tue, 11 Feb 2014 11:40:30 +0100
From:	Torsten Duwe <duwe@....de>
To:	Raghavendra KT <raghavendra.kt.linux@...il.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Anton Blanchard <anton@...ba.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Scott Wood <scottwood@...escale.com>,
	Tom Musta <tommusta@...il.com>, Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linuxppc-dev@...ts.ozlabs.org,
	Raghavendra KT <raghavendra.kt@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2] powerpc ticket locks

On Tue, Feb 11, 2014 at 03:23:51PM +0530, Raghavendra KT wrote:
> How much important to have holder information for PPC? From my
> previous experiment
> on x86, it was lock-waiter preemption which is problematic rather than
> lock-holder preemption.

It's something very special to IBM pSeries: the hypervisor can assign
fractions of physical CPUs to guests. Sometimes a guest with 4 quarter
CPUs will be faster than 1 monoprocessor. (correct me if I'm wrong).

The directed yield resolves the silly situation when holder and waiter
reside on the same physical CPU, as I understand it.

x86 has nothing comparable.

	Torsten

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