linux-kernel - Re: [RFC PATCH 0/2] ARM: Remove any correlation between IPC and BogoMips value

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Message-ID: <20130507090849.GC25387@mudshark.cambridge.arm.com>
Date:	Tue, 7 May 2013 10:08:49 +0100
From:	Will Deacon <will.deacon@....com>
To:	Christopher Covington <cov@...eaurora.org>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Marc Zyngier <Marc.Zyngier@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/2] ARM: Remove any correlation between IPC and
 BogoMips value

On Mon, May 06, 2013 at 07:01:23PM +0100, Christopher Covington wrote:
> Hi Will,
> 
> On 05/03/2013 01:35 PM, Will Deacon wrote:
> > Hi all,
> > 
> > This small patch set may look a little over a month late, but there is a
> > serious reason for posting it.
> > 
> > When I moved the ARM delay loop over to using the architected timers
> > rather than the CPU spinning loop (which has all the problems associated
> > with cpu frequency scaling and what-not) I thought I was doing something
> > useful for the port. However, it turns out that a surprising number of
> > people have complained, and continue to complain, about the drop in
> > their `BogoMIPs score'.
> 
> Have you considered adding the old code back in, but in a form that's not at
> all referenced by the delay loop code and just calculates CPU-based bogomips?

That seems like a lot of effort in order to preserve something that isn't
even meaningful. We might be better just zeroing the value, but then we'll
inevitably get bug reports of it being `wrong'.

Plus, the calibration during boot introduces a brief delay when onlining
each core whereas this can be skipped when using a constant timer.

Will
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