linux-kernel - Re: [PATCH 7/7] Simple Performance Counters: SLUB instrumentation

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Message-ID: <Pine.LNX.4.64.0708171338440.9404@schroedinger.engr.sgi.com>
Date:	Fri, 17 Aug 2007 13:39:56 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/7] Simple Performance Counters: SLUB instrumentation

On Fri, 17 Aug 2007, Mathieu Desnoyers wrote:

> Why do you printk inside the timing period ? Filling the printk buffers
> or outputting on things such as serial console could really hurt your
> results.

It was easier to code?

> I hope you run your system with idle=poll and without frequency scaling
> at all, because otherwise your cycle count would be completely off on
> many AMD and Intel CPUs. You can have a look at this (very rough)
> document on the topic: 

The cpu will definitely not be idle during these measurements and no 
frequency scaling is active.
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