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Date: Sun, 13 Apr 2008 23:51:50 +0200 (CEST)
From: Erik Bosman <ejbosman@cs.vu.nl>
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To: "H. Peter Anvin" <hpa@zytor.com>
cc: Arjan van de Ven <arjan@infradead.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
       Andrea Arcangeli <andrea@cpushare.com>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] x86: Implement prctl PR_GET_TSC and PR_SET_TSC
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On Sat, 12 Apr 2008, H. Peter Anvin wrote:

>
> I also saw no mention about performance impact, which need to be
> considered whenever *anything* is proposed to be inserted into a hot
> path.  It may be (heck, *should be*) that the performance impact isn't
> measurable, but that needs to be positively established.
>
> 	-hpa
>

It took me a while, but I have done some tests om my system with and
without my patch applied.

All deamons but klogd/syslogd were shut down andI used the following
command:

LMBENCH_SCHED="SINGLE" \
/usr/lib/lmbench/bin/{i686-pc,x86_64}-linux-gnu/lat_ctx -s 0 2

The variation was quite high so I ran it a 1000 times for each
configuration.

x86_32, patch applied,     1000x repeated, avg: 1.319, rmse: 0.081
x86_32, patch not applied, 1000x repeated, avg: 1.335, rmse: 0.107

x86_64, patch applied,     1000x repeated, avg: 1.417, rmse: 0.0716
x86_64, patch not applied, 1000x repeated, avg: 1.423, rmse: 0.0745

This is on a core 2 duo E6300.

Erik