linux-kernel - Re: [PATCH 2/3] x86: Implement prctl PR_GET_TSC and PR_SET

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Message-ID: <Pine.GSO.4.56.0804132320260.6537@keg.few.vu.nl>
Date:	Sun, 13 Apr 2008 23:51:50 +0200 (CEST)
From:	Erik Bosman <ejbosman@...vu.nl>
To:	"H. Peter Anvin" <hpa@...or.com>
cc:	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Andrea Arcangeli <andrea@...share.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] x86: Implement prctl PR_GET_TSC and PR_SET_TSC



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
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