From: Vince Weaver <vincent.weaver@maine.edu>
Date: Mon, 20 Apr 2015 10:42:56 -0400 (EDT)
To: Andy Lutomirski <luto@amacapital.net>
cc: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>,
        linux-man@vger.kernel.org, linux-kernel@vger.kernel.org,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Paul Mackerras <paulus@samba.org>, Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Stephane Eranian <eranian@google.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Kees Cook <keescook@chromium.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        "hillf.zj" <hillf.zj@alibaba-inc.com>,
        Valdis Kletnieks <Valdis.Kletnieks@vt.edu>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [patch 10/10] perf_event_open.2: 4.0 update rdpmc
 documentation
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On Fri, 17 Apr 2015, Andy Lutomirski wrote:        
> On 04/16/2015 11:20 AM, Vince Weaver wrote:
> > Probably a better change would have been to add "2" to mean per-process
> > and make that the default setting.  Probably too late to fix that now.
> 
> Good point.  I wish you'd thought of that sooner :(

Well it's been a busy semester and so I've had less time than normal to 
play perf_event ABI police.

I also was surprised this particular patch managed to get into 4.0 so 
quickly; I thought it was going to be a 4.1 change when I added it to my 
"changesets to look at more closely" list.

In any case most people won't notice this change.  It will be a minor 
inconvenience for HPC people doing complicated homebrew self monitoring
(especially if RHEL backports the patch and then suddenly things break and 
a simple "well are you running 4.0 or newer" is meaningless). Using
the value in /sys/devices/cpu/rdpmc to help debug the problem wouldn't
have worked anyway because it looks like non-root can't do that.

Vince
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