linux-kernel - Re: [PATCH] [1/3] Provide rdtscll() asm/msr.h for user space

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Date:	Tue, 07 Oct 2008 16:25:00 -0700
From:	"H. Peter Anvin" <hpa@...nel.org>
To:	Andi Kleen <andi@...stfloor.org>
CC:	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [1/3] Provide rdtscll() asm/msr.h for user space

Andi Kleen wrote:
> 
>> I would suggest writing a <sys/tsc.h> header file and submitting to the 
>> glibc people, instead, or perhaps even better, start a libarch/libx86 tree.
> 
> That wouldn't work on old kernels. asm/msr.h has been the traditional 
> interface for this and rdtsc has worked forever (at least dating back to 2.0)
> rdtscll is a bit newer, but still in Linux terms ancient (2.4)
> 

It would definitely work on older kernels.  Just don't stomp on the 
kernel's namespace and you can do whatever you want.

> Also in my experience distributions are extremly slow at keeping up
> with glibc, so even if this was added to glibc it would be probably
> years before it would be actually usable :/ And I see about zero
> point in changing a perfectly fine include name breaking everything old.

So ship the include file with your utility.  Hardly a big deal.  But 
yes, that's part of why I'm mentioning the idea of putting it in a 
separate library, which can also house other low-level constructs.

> Anyways if you insist I can probably deal without
> but I (and likely others) would think something nasty about you every time 
> I have to cut'n'paste that code again. Do you really want to risk that? @)

If you're really incapable of maintaining a single user-mode header file 
with a handful of one-liners in a sane way, then definitely.

	-hpa
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