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

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Message-ID: <48012002.8030701@zytor.com>
Date:	Sat, 12 Apr 2008 13:48:02 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Arjan van de Ven <arjan@...radead.org>
CC:	Erik Bosman <ebn310@....vu.nl>,
	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

Arjan van de Ven wrote:
> 
> Hi,
> 
> why did you make this a configuration option? In general it's not
> a good idea to make userspace visible ABI's (PR_* clearly is one of these)
> a CONFIG option unless there's some HUGE space saving going on.
> I don't see that here....
> 
> So can you explain your rationale for making this a config option?
> 

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
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