Date: Tue, 11 Feb 2014 11:40:30 +0100
From: Torsten Duwe <duwe@lst.de>
To: Raghavendra KT <raghavendra.kt.linux@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>, Anton Blanchard <anton@samba.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Scott Wood <scottwood@freescale.com>, Tom Musta <tommusta@gmail.com>,
        Ingo Molnar <mingo@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linuxppc-dev@lists.ozlabs.org,
        Raghavendra KT <raghavendra.kt@linux.vnet.ibm.com>
Subject: Re: [PATCH v2] powerpc ticket locks
Message-ID: <20140211104030.GG2107@lst.de>
References: <20140207165801.GC2107@lst.de> <1392001823.3996.21.camel@pasglop> <CAC4Lta2Pssu5QY_QLmy5C3Fm2G3fwpiuc5BNOLBnQTmmRH+W4Q@mail.gmail.com>
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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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