linux-kernel - Re: [PATCH 3/5] metag: smp: don't spin waiting for CPU to start

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Message-ID: <alpine.DEB.2.02.1307012342500.4013@ionos.tec.linutronix.de>
Date:	Mon, 1 Jul 2013 23:46:00 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	James Hogan <james.hogan@...tec.com>
cc:	linux-kernel@...r.kernel.org,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Subject: Re: [PATCH 3/5] metag: smp: don't spin waiting for CPU to start

On Mon, 1 Jul 2013, James Hogan wrote:
> Use a completion to block until a secondary CPU has started up, like ARM
> do, instead of a loop of udelays.
> 
> On Meta, SMP is really SMT, with each "CPU" being a different hardware
> thread on the same Meta processor core, so as well as being more
> efficient and latency friendly, using a completion prevents the bogomips
> of the secondary CPU from being drastically skewed every time by the
> execution of the tight in-cache udelay loop on the other CPU.

The least of our worries is the correctness of bogomips. But if that
patch makes bogomips less bogus while fixing a real issue, please add
my
 
Acked-by: Thomas Gleixner <tglx@...utronix.de>
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