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

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Date:	Sat, 26 Apr 2008 15:47:35 -0700 (PDT)
From:	dean gaudet <dean@...tic.org>
To:	Erik Bosman <ejbosman@...vu.nl>
cc:	Michael Kerrisk <mtk.manpages@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrea Arcangeli <andrea@...share.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH 2/3] x86: Implement prctl PR_GET_TSC and PR_SET_TSC

On Mon, 14 Apr 2008, Erik Bosman wrote:

> 
> 
> On Mon, 14 Apr 2008, Michael Kerrisk wrote:
> 
> > Erik,
> >
> > Could you CC me please on kernel-userland API changes.
> >
> > Also it would be helpful if you could provide a short paragraph
> > (plaintext is fine) that describes the new commands and would be
> > suitable for inclusion in the prctl.2 (
> > http://www.kernel.org/doc/man-pages/online/pages/man2/prctl.2.html )
> > man page -- would that be possible?
> >
> > Cheers,
> >
> > Michael
> >
> 
> .TP
> .B PR_SET_TSC
> (Since Linux 2.6.??, only on x86)
> Set the state of the flag determining whether the timestamp counter
> can be read by the process. Pass
> \fBPR_TSC_ENABLE\fP to \fIarg2\fP to allow it to be read, or
> \fBPR_TSC_SIGSEGV\fP to generate a \fBSIGSEGV\fP when the process tries
> to read the timestamp counter.
> .TP
> .B PR_GET_TSC
> (Since Linux 2.6.??, only on x86)
> Get the state of the flag determining whether the timestamp counter
> can be read from \fIarg2\fP.

i might be too late... but shouldn't these #defines be PR_SET_RDTSC and 
PR_GET_RDTSC or something like that?

to me calling them PR_SET_TSC/PR_GET_TSC just seem like alternative ways 
to change/get the TSC (and could even reduce to portable TSC 
implementations... since such registers do exist on other architectures).

-dean
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